"That makes sense , but after 30 years running I can't tell any wear.
And my bores still have the hone marks. Compressors are not like cars
where gas contaminates the oil... "

Good point.

I would consider the missing acidic component and frequency of oil
changes would help extend a compressor life.

I do know that in gear head lathes they also want non detergent oil so
any abrasive material settles to the bottom of the gear case. It might
be a good idea to use a magnetic drain plug in the bottom of the
compressor case to contain any abrasive particles. I have seen magnets
glued in the bottom of gear cases of lathes and they do collect
abrasive particles.

TMT