I have some reservations about the use of PPCo's 320 or any other glue
to fix capstans in position.  Capstan screws are adjustable for a
reason: for one thing, they compensate for compression and wear of the
leather and felt in the action.  One can notice the effect of this wear
by looking at the felt on the let-off button of an upright action, and
then turning the button.  By merely making one full turn, which doesn't
translate into much vertical motion, let-off will change significantly,
and then almost return to the original setting when the jack again
contacts the packed spot on the felt.

There are other circumstances in which capstans and other adjusting
screws need to be turned up or down.  Granted PPCo 320 glue looks like
pretty useful and benign stuff, and might come in handy where the
adjusting screws are really losing their grip.  But I'd rather not
introduce any unnecessary material into a piano.  My feeling is that
any involuntary turning of screws is not the big issue.  If it were,
the manufacturers would have found some method of locking capstans,
etc. in place, rather than merely relying on the screw threads.

Richard Friedman