Not sure you should have a pass through terminator.  Usually termination needs to be after the last device used.  That was usually why it was referred to as a scsi chain.

Have not had time to read the other post but of course if it has not been cleaned and recapped motherboard I would not try and diagnose anything.

If you are good in that like my first suggestion termination at the end is where it should be.  Never saw very pass through terminator, my guess is that would be why.

There has always been SCSI magic, so take it with a grain of salt, after over 20 years the drives being iffy only makes it worse.