Dear Mike, I have a smaller version of this gen-set MDJE 7.5 KW on an 1981 Silverton 37 convertible. The beast of a machine rattles like hell when running. It sounds like hammer beating an anvil (this was an actual quote from the Onan rep. Seems they were made for Tanks in WWII. Noise wasn't an issue. At any rate I had the same leak....it started small until one day it would just not hold any oil at all. The oil pan is cast iron and the drain tube is just black iron pipe. As you look at it (I had to pull the gen-set to finally see it) it will appear that the drain pipe is beating against the drain pan. Over the years it will just crack on the threads. See if you can unscrew the drain pipe and check the threads for a crack. Mine was about an 8th inch gap. I cut off the bad threads, turned it around and used it again. I figure I should get another 23 years out of it. (the damn things never seem to die) Hope this helps. J. Peter Zimmer