OK. Big leak from the front of the engine. My theorized culprit was the oil pump. So I pulled the engine and fan housing. Not the oil pump. Rather, the source of the leak was via the threads of one of the top fan housing studs. Its threaded hole opens into the crankcase breather cavity. It's clear that this will leak unless the threads are sealed somehow. What kind of sealant should I use?

The one on the upper drivers side opens to the oil fill tower. Never heard of those leaking, but I could see how. It's not a pressure zone, so anything should work fine. I would put Loctite 518 on it, since I have that here. But Loctite 565 (liquid teflon) would work. Gasgacinch would work. Loctite threadlocker would work as well. Just not RTV/Silicone style sealants.

Thanks, McMark. I've got the blue Loctite here, so I think I'll use that. Loctite says it will work as a thread-sealant and is oil-tolerant.

I would be bothered by the "big leak" remark. As that is normally not a high pressure place, what caused the big leak?
Please check:
1. higher then normal pressure in the crankcase (bad rings)
2. Cracks in the case around that stud.

Yeah, OK, I'm overstating. It's not really that 'big'. It's just enough, over time, to run down the fan housing and wet the bottom of the engine.