A few thousand miles ago, I began to get occasional whiffs of a "hot smell" in the cabin. At first I thought a raw exhaust leak, but it didn't happen with a cold engine. It somewhat smelled like burning rubber, but there weren't any rubber parts getting that hot either. The smell would go away if I put the cabin heater on recirc. I also noticed oil consumption had increased slightly. Next time I had it up in the air, I looked around and saw part of the exhaust manifold damp with oil.
This leak is NOT
from the cam cover gasket, as it is completely dry up above the manifold. It also is not coming from a valve stem seal. In order for that much oil to appear outside
the manifold, it would need to be puking enough oil into the exhaust to fumigate the whole neighborhood. The oil is definitely coming from around one stud, then running down the manifold until it burns off and makes a bad smell.
The nut is seized solid to the stud, so both came out when I tried to unscrew it. Stud was damp with fresh oil. Here's a pic with the stud removed showing the oil dampness:
I can't get a very good angle on it and the focus is terrible, but I got my inspection camera up there to see the far end of the stud hole damp with oil, suggesting a tiny crack or defect in the head allowing oil to seep out.
At first I tried using oil resistant RTV to seal the stud, but it would largely get squeegeed off as the stud screwed in, and the leak would return in a few weeks. I cleaned the threads very thoroughly with throttle body spray and a pipe cleaner each time, but the RTV was just not meant for what I was asking of it.
I just put it back together with Permatex High-Temp Thread Sealant, so I'm hoping that provides the fix I've been looking for. Sealant is meant for threaded fuel, hydraulic, coolant, and oil fittings and withstands 400F / 204C.
This is less a question thread and more of a chronicle of my attempts to repair this problem plus follow ups. Feel free to add any tips you may have. "Do it right - replace the entire head" and "old car - let it leak" are not acceptable in this case.