Old Part Numbers: A19714, D27022Check Valve, 1/2" male NPT x 1/4" hose barb. If your compressor constantly leaks after it shuts off, this is probabably the problem. If this one-way check valve is clogged or defective, air will backfeed from your tank, so...

Screw that fastens the front and back of the belt  guard to each other, and to the compressor base. THD FORMING

Old Part Numbers: D20675, AC80-BQuick-connect coupler, 1/4" male NPT x 1/4" body.

1/4" male NPT x 1/8" female NPT brass bushing reducer for air compressors.

Old Part Numbers: A14877, N044990, SS-1286, 5130029-00, 5131153-001/4"-18 x 1" male NPT close pipe nipple. For model D55167 type 1 & 2 and others. Remember to apply plumber's tape to the threads.