I bought a field rebuild kit for my compressor, I have not done it yet as the oil leak I was looking for was an oring on my pump..maybe this winter. I purchased from ebay around 90 bucks gaskets and valves, no pistons or rings. I guess it only the head.
The air compressor on my bus was working slow and I was having a problem getting one so I tore the head off and the valves were gunked up with carbon so I cleaned it up, made a head gasket (it was only paper) and put it together and worked fine.