I have two Wheelock grands of similar vintage with the A/B system and
you should be aware that the B drawer does not shut off immediately
like the A and other systems.  It has a constriction in the pneumatic
under the start switch and it closes the pneumatic very slowly so that
if you wait 10 seconds after the roll leaves the take up spool it
should go off.  Are you sure you are not just being impatient for shut
off?

When the repeat is on, the rewind slows down when it nears the end of
the roll and it does not go far enough to unhook from the take up
spool.  The lag in shut off allows it to replay, then closes the take
up spool hole which stops the shut off pneumatic moving.  Does yours
slow down on rewind?

You can check the shut off pneumatic it is just below the switch and
it is tubed to the take up spool by way of the switch.

I sure do miss the subdued/brilliant switch on the B drawer.

D. L. Bullock   Piano World   St. Louis