Check Part to Insure Piston does not Seize
We now know that the spacer tube on the upper shaft had too tight a tolerance and that's what is causing these compressor seize ups. There was some variation in them going from loose and sliding easily, to tight but still sliding. If your worried about your compressor suddenly quitting one day, then it would be a good idea to check this spacer tube now before issues come up.
If you look at the exploded view diagram, its part #7. Remove the upper cylinder, unscrew the hollow set screw (#11) and then you should be able to hook the spacer and pull it out. Check to see if it slides easily on the piston shaft. If it does then great, reassemble and your done. If it seems pretty tight, let me know here and we will send you out a replacement.
Thanks for all your cooperation on this.