I was able to read a tape this morning, after pulling the drive apart
and making sure every last trace of the old pinch roller was cleaned
from the shaft. The motor runs HOT (which explains why
the old rubber
which was already soft liquified) and any little bit left will
contaminate the cartridge.
It is also souluble in isopropyl alcohol.. So be careful if you try
to clean a tape head with a surviving (unlikely..) roller.
It is a block-addessed device (like DECtape II's).
So that it is saved somewhere, here are the specs:
3M MCD-40 rev 4.0 firmware (Apple Tape 40SC)
4848 blocks 8192 bytes/block (39714816 bytes total)
The drive always retensions when you put in a tape.
It will then do the usual tape head positioning, pause,
then do one last read before extinguishing the red light.
If the light flashes, tape loading failed.
I've put some emails out to people I know who might have
the actual specs/pgmg info, but I'm doubtful that they
saved it.