Hello all,
  My D25U engine oil is diluted with diesel. Have any of you experianced this and what is the entry point you have found to be the culprit? Thanks in advance for any help you might give me.

A lot of threads on this. Use the search engine. Most have to do with Fuel Transfer “O” Rings-at least on D4’s. I didn’t have the problem but disassembled and used the threads extensively.

Here is an example, I'll keep searching:
"D2 5U diesel in oil was created by beaver-flat"

Good Luck-
Bernie

To make certain we are talking about the right things please give the SE#. First check the small drain tubes down by the transfer pump to make certain they are clear. If the leak in the transfer pump is not too bad they should let it drain out there. Check to see if you have leakage there which indicates the transfer pump may be the culprit. However, it might and most probably is being caused by a leaky seal that is between the injection pump and the fuel tower. They are notorious for leaking fuel into the oil. Not too bad to fix but you do have to remove the injection pump to replace it and while at it you might as well replace a couple of the other shaft seals while you have it open. Someone probably has pictures of what is referenced above.
Good luck.

Ok, thanks. I appreciate your help!