Tim,
I had a similar intermittent problem that started out with quarter sized drops of fuel oil spotting my garage floor. At first, I could determine only that the fuel was dripping down the crankcase breather tube. Before leaving on vacation, I took my '97 3500 to the local dealer who couldn't find anything wrong. By the time I got to Maine, I had diesel fuel all over the back of my camper. I discovered the problem in a parking lot when I shut the engine down... . the oil was spraying from behind the fuel primer button on the transfer pump(?). I explained this to the dealer there and he couldn't get it to leak. When I refused to drive the truck further, he finally agreed to fix it. Oddly enough when they drove the truck into the newly painted bay to replace the pump uner warranty, it sprayed oil all over there as well... a quart or more as I recall. I've seen reports on this site where it is possible just to replace the rubber o-ring behind the fuel primer button, however, in my case they replaced the entire pump assembly. I suspect it had something to do with the change in fuel pressure that causes the leak as initially it seemed to leak only at startup or shut down. Hope this helps.
Tim