It's listed as a needle bearing in the parts diagrams, so I don't think that could be the source.

In the meantime, I've adjusted the valves and cleaned up the valve cover before replacing it. The cams were in great shape! And the valve adjustment wasn't nearly as difficult as I had expected -- but I'm glad I shelled out for some bent wrenches. I've also been removing and cleaning up the engine accessories. The water pump + housing looks OK -- some scale on the inside that should come off with a citrus flush. The vacuum pump is the old style used in the W110, and I can't find a source for diaphragm repair kits that isn't <$150 shipped -- yikes! I might see if a junkyard 240d vacuum pump fits to make future repairs easier. Since this bus is so bare-bones, the only thing using vacuum from the pump is the brake booster. The shut of valve on the fuel pump looks like it uses vacuum from the intake manifold instead of the pump. Is this true for the other diesels, too?