rider fan is correct.... the company I owned used to rebuild these compressors and I can share that 80% of the units returned to us as cores had no issues other than some other issue in the air system that was in correctly diagnosed... I've not read enough in this thread to offer more information.....
Except that... I'd like to know what the first problem was... that required the replacement of both the drier and the compressor...
Retired Business Owner, Re-manufacturing HD Clutches, Brake Shoes, Air Compressors, Sales & Installation of PacBrake and other Industrial Friction