Concerning Welte adjustable screw bleeds that collect dust so fast:
I was wondering if anyone ever tried using McLube on the screw tip to
lower drag and possibly lessen the collection of dust on the screw and
or bleed hole.

McLube is an industrial Mold release agent that is suggested by
Steinway to use on key bushings on all new Steinways, to be applied
by the dealer's technician.  I do not know why the factory could not
use it... or perhaps they do by now.  McLube is available from Pianotek
Supply Co.  It lays down a dry coat of Teflon on the surface or in the
felt.

D. L. Bullock   the Piano World    St. Louis