I've rebuilt a couple of small shop-sized piston air compressors and have some modest expertise in the area. Parts for air compressors tend to be high to high as hell. Question then is whether it makes sense to rebuild/repair or replace. For most industrial use in smaller sizes of piston compressors my best guess is that for most people you are better off getting a new pump--they cost, but there's a lot to be said for new parts with no fatigue life problems. Can't help you any with any other style of compressor. For lighter use or tight budgets it may make sense to rebuild a piston compressor--general parts needing replacement/repair are rings, bearings, and valves/valve plate assemblies. Price all those out--be sure and check wristpin to piston and rod clearances--you may need new pistons. As is often the case, the parts people at the dealer are generally quite knowledgeable and helpful in matters like this
