OK, I went to the guy I call Obi Wan. He is about the last step on the ladder for power gen knowledge. I copied a few posts from Triple Jim. Sent them off to Obi Wan. I will copy and paste the posts from Triple Jim, my post to Obi Wan and his reply. I really wish I could use his name, but he still works for the gov. May not be good. So for the time being that's how it is. I did not include the CC line, mentioned in Obi Wan's answer, but do know the man fairly well. As stated, he is one of three of the big honchos in the Engineering Dept. If him and Obi Wan both agree, its the word I would live by.
First message from Triple Jim:
I got to thinking about this no-idle rule for the MEP-002A and MEP-003A. The regulator controls the exciter's field by applying current to the control windings of CVT1. When current is applied, CVT1 reduces its output to the rectifier bridge A4, and current to the exciter windings is in turn reduced. If the engine is run at idle, or speed lower than 1800 RPM, the AC output of the generator is reduced, and the regulator board will try to bring it up. It does this by reducing its output to control windings of CVT1 so that CVT1 is at maximum output. This means that the output transistor of the regulator board is working the least when trying to increase the output of the generator, and is least likely to overheat and fail.
Maybe other generators with a different scheme of regulation do indeed stress their regulators if the engine is run slowly, and maybe the recommendation of not idling them for more than a few seconds is valid for them, but it looks like that problem is not present on the 002 and 003. I have no doubt that output transistors fail on the 002 and 003 regulators, but it would be more likely for that to happen from running the generator unloaded, forcing the regulator to work hard to keep the output down.
Sometime soon I plan to run my MEP-003A at idle for a while, shut it off, and feel the regulator's output transistor. I'll let you know what I learn, but I have no doubt that it will be cool.
Second message from Triple Jim:
OK, I just ran my MEP-003A. First I disconnected the output of the main transistor at terminal 17 of the regulator board. This terminal sinks the current through the exciter field control transformer CVT1 supplied from terminal 14, which is in turn supplied by rectifying diodes CR6 and CR7 (maybe CR8 and CR9 in some boards), which are supplied AC by T1. I connected a Fluke 87 meter between wire X39C16 and terminal 17 so that it reconnected the wire and read the current that the main output transistor was carrying.
Then I started the generator as usual, running at 1800 RPM. The current was about 230 mA to keep the output at 240 Volts. Then I reduced the engine speed with the governor cable as low as it would go. This really isn't what I'd call idle speed, but it's considerably slower than 1800 RPM. The current went down to 130 mA. After letting it run like this for a couple minutes, I stopped the engine and felt Q3, which is the big transistor on the board. It was about the temperature of everything else in the control box... cold.
This is not a recommendation that everyone go out and idle his MEP-002A or MEP-003A. I do hope it provides some information and dispels a myth. As I said above, there may be other reasons that it's not good, or even bad, to idle these generators, but so far all I've thought of is that it wouldn't be good to do it while a load is connected.
Also, as I said above, only the MEP-002A's -12 "OPERATOR AND ORGANIZATIONAL MAINTENANCE MANUAL" has the warning against idling, the MEP-003A's comparable manual does not.
I have no doubt that Q3 sometimes fails, and I'm sure that's not the only component on the board that does, but at this point, I do not believe that Q3 or anything else in the regulator will be damaged, or even stressed, by idling.
My email to Obi Wan:
Obi Wan,
I darken your door once again. The above text is from a guy I know who has built and sells AC and DC volt regs for the -002A. Once again we were chewing the rag about idling the gen sets. Since 1973, It's been drilled into my hard head not to do that. The guy who wrote these messages tends to disagree. The second message was his test results. Is there a good reason to not idle? Or not? If so, why?
Obi Wan's answer:
CLASSIFICATION: UNCLASSIFIED
Guy!
I used to idle those things too. Grew up on the farm. Made sense to assist the engine and lube systems like all other engines. I was also a hard Headed dumb as*. Just ask my wife, she can tell you.
Unfortunately, the following occurs. The regulator continues to try to keep output voltage at set levels, usually 120/208VAC (today operators do not remove the load and wonder why the fault comes up from extra exciter current and voltage). Loaded or not, in order to do that as the man says the regulator increases the exciter voltages so to keep the main gen output. He also figures incorrectly that the current goes down. That saw toothed wave acts like AC before the diode board and inductance kicks in. CERDEC tests indicate this increases transistor current while the transistor PIV is reached and regulator action and the current thru the external Diode board. Current heats up these devices. It also made more sparking on slip rings and brushes in the old diesels. I changed enough regulator transistors on the next diesel generation and when I mentioned it, " to just shut it down", I changed less of them. I was now a turn coat. Traitor. Supply demands show more components used costing more tax dollars if you idle them down. Double whammy and I had to eat crow. Had an old Crusty Warrant Officer who yelled at me a lot over that idling thing as he eventually told me the same as I am telling you. Thus a decision was made before the new DED gens hit the active force while we had the post-Vietnam diesel 15-60 KWs and the gassers to just shut them down. I had all gassers and it hurt nothing I ever had. I was at SHAPE in late 70s now the Supervisor and burnt out the regulator transistor and had to change it losing my sleep period during an exercise idling it down at no load on a MEP-006. The one before the 006A. It was on loan. You find the same with precise gens especially. They figured that crap all out because of a turbine generator repairer, who must remain nameless, but had a reputation of knowing the systems. Thus his supervisor (old B*stard Warrant Officers as Mata put it ) had the CERDEC tests done(CW3 ****** later CW4). Your colleague needs to just contact Caterpillar power and ask and they say the same thing independently of US ARMY. Cummins power says the same thing. Several of the issues we had in the WAR zone on civilian gens were the from the idling issue as units destroyed the regulators in a bunch of them. Solid state don't seem to play with that stuff very well. Oh well, getting back to the 70s, Resolving the fight CERDEC results were published quieting everyone in those days at Belvoir. I thus after that one became one of those Warrant Officers like you did. I was proved wrong as I idled them down. Helps engines, bad for regulators and external diode boards, costs more money to run the gens. I was hard headed. Turbines did not idle, just unloaded but the RPM stayed the same at around 42,K RPM. Should have realized the same for diesels but I was a dumb as* 52F3H. Anyway TQG gens were more touchy about that but I was already a converted fixer since 1979.
I can say I have had many chopper rides being shot at because operators of 002A-006A gens did not know they had to pull out the speed control. They figured once set at 60 HZ and their loads did not change they did not need to play with it and once not taught to younger Soldiers it lead to not operating correctly leading further into laziness as to today where over 90% are no longer licensed, and no one cares. Toasting a Soldier is not my idea of a good day and it is coming.
In the CC line is one of the three leads of the engineering department. I'm sure he has more but it is much easier to just say to, "Run no load to cool down the main gen and then; just shut em down"
At this point, my best guess is that running the generator at high load at well above 60 Hz would be most likely to stress the regulator's output transistor. In this case, the regulator would have to send a lot of current to CVT1 in an attempt to hold the voltage down to the setpoint. 
