Thanks for the responses. I had kind of ruled out the vacuum pump since it feeds the intake with a clear hose and there was very little that looked like oil stuck in the hose, but there is some. I think I will explore that further, it does sound like the most likely explanation. I will let you know what I find.

Regarding the compression, it is a cheap gauge. I don't trust the accuracy of the absolute numbers, but relative to each other the numbers are close, so no single cylinder appears bad.