So I split the engine case of my vintage VW the other day:
So I found out what was putting the grit in the oil. I had used a crappy after-market distributor distributor clamp. The distributor is what holds the distributor drive shaft in the case agains the motion of the crankshaft, which is turning it but always trying to push the shaft out of the case. If the shaft gets too high, it eats up the brass gear on the crankshaft that's turning it.
That brass gear is toast, about 20% of the gear is gone. So I need a new one. And I'll replace a lot of other stuff in the engine. I got out my micrometers last night, and the camshaft is pretty badly worn too.
So I'm going to do a more thorough re-build than I had been contemplating. I'll add an oil filter to get the maximum amount of life out of it. I have other parts on order, I just need to find a machine shop that will regrind the crank.