The mechanics story is the same as mine.
He doesn't know what's wrong now and he said so.
Most of the details came from him directly other than what I observed later myself when I went to pick up the car and found it undriveable and knocking.
I would never put used oil (despite filtering a bit as he claims) from some other motor into another persons car. That has me worried, as does the engine knock that was never there before.
This is a quiet, well maintained car.
The oil has always been clear and it doesn't burn any between oil changes.
I checked it the day before he worked on it and it was fine.
The vehicle doesn't use any oil or antifreeze.
I was being proactive to fix a small leak visible only as a wet area near the intake manifold.
Update: Friday 1pm he pulled the oil pan and found some type of soft debris,,, maybe old gasket material (he's not sure what it is) clogging up 60% of the oil filter inlet screen. He cleaned that off and reported that the bottom of the oil pan was quite clean, with the exception of chunks of gasket material or something.
I think would be a good idea to also check the condition and cleanliness of the oil pump while the pan is off.
We'll see.