You will likely need new rings and a new cylinder. There will typically be where to both the piston and the cylinder. You will need to open up the compressor and inspect it. It there are any scratches on the cylinder wall it will definitely need to be replaced. At minimum a machine shop should hone the cylinder when new rings are installed.
The piston rings are part numbers; #17153, #17158 and #17163. The cylinder is part #17328. All of these parts are available from http://www.ereplacementparts.com.