If the problem is mechanical, I will be relieved - so I'll putz around with the head pressure for a while and see if I get a resolution. Remember this drive reads and writes to one logic board, but not to two others. I suppose its possible the MacII series SWIM chips run to a slightly more tolerant read signal or put more current through the buffers somewhere.

My worry was that some electronic component on the drive itself might have failed or gone off spec, weakening the signal. I've ordered a schematic for the Sony 880k drive from Bomarc, but last I heard he was still burrowing through a snowdrift in Wyoming trying to get to the post office. :-/