theres no oxygen sensor on a 2004 5.9 cummins diesel, the motor is just a common rail using a CP3 belt driven fuel pump, the injection system is computer controlled. A diesel engine will run on used motor oil, transmission oil, straight vegtable oil(heated) bio diesel, diesel fuel and the list goes on and on. The problems with diff fuels are lube, BTU's of the fuel, corosion and coking of injectors. On straight WVO I have heard more stories of coking on injectors. No matter what fuel you use you would want to ensure the fuel is filtered very well, you can purchase filter socks for waste veggy oil, on my bio diesel processor I use filters in the system of 1 micron both socks(which are cleanable) and canisters. The smallest particles can cause very large problems in a diesel injection system even the mutifuel duece. Second water is a issue, but you can settle much of this out. I really would suggest you do a little research on sites such as greasecar.com
www.vegvw.com, and others. Theres a ton of info there and it should really help with the ?'s. But as far a a 6.2 detroit with a stadyne injection pump having problems with WVO or bio diesel there should not be any issues with the exception of rubber lines swelling. and the M35 will also have the same issues. A great write up I jst thought of is
http://www.fryoil.org/ , they converted a 6.2 diesel to WVO and disscuss maint, and other areas. REmeber that WVO will have to be heated to 175 deg's and that requires a 2 tank setup that will allow you to start motor on diesel(or bio diesel) and then use the vehicles cooling system to preheat the oil then switch to the wvo and run the truck then before shut off purge the system back on diesel(or your injection pump will have a mess in it, just like grease in a pan after it cools). This is why I went with straight Bio diesel, alittle more work but well worth the results, I make mine at the cost of .60 cents a gallon. and run it in every diesel motor i have.