The idea of pulling the dash to replace the motor is really the last
thing I want to do.

Your motor is fine.  The arms are designed to fail this way on overload to
protect the rest of the linkage.

Pick the metal carefully out of the splines on the shaft.  If this has
never happened before that may be all you need to do before remounting the
arm and torquing to the Bentley spec -- do not exceed or you can open a
world of pain.

Probably it has happened before and you have to add a 7mm washer (or a
bored-out one) so the nut doesn't bottom out before the new splines are
fully cut.

If it's happened more than once you may also have to relieve the entrance
to the opening in the arm to keep it from fouling the shaft below the
splines.

Yrs,
d