The only other thing I can think of might be the reed valves in head. Sounds like it must be oilless. Oilless compressor are almost always direct drive (no belt).
Wookie does sound like it has seized. May have overheated or run low on oil. Sounds like it probably isn't worth fixing. Could keep tank though, parallel it with another compressor to obtain more volume.
You're better off to stay away from the oilless compressors, they seem to wear out quickly.
