I bought my first one and it puddled everyplace it went. The local Sheriff's Office had been using it for jail maintenance and a snow plow truck. They told me it had an oil leak. After putting on a new flex plate and getting he starter rebuilt, I started to pursue the oil leak. It was diesel fuel.
The lift pump was dripping into the front cross member, the fan was picking it up and blowing it back on the pan and it would run down the pan rail to the back of the block, where it would drip off the rail on to the pavement. It always looked like black runny oil from all of the dirt diesel seems to attract. When it dried though, it was like a bunch of black rings, instead of a thick oily spot like you would get from engine oil.
Just something else to check out. The pump is a pain to change, the hole is small and there is a push rod from the cam to the pump arm, just like the small and big block Chevrolets used. I usually coat the rod with lithium grease and stuff it back in the hole before trying to install the pump. Failure to get the push rod back up in the hole will result in a damaged pump and bent push rod. Glen