I thought I should pass on my experience with my Weber D.A. 5'8" made
in 1926.  I inspected the wiring where connections are made and all
looked fine.  I cleaned the switch, rubbed the oxide off the plug
prongs, cleaned them with pure alcohol, replaced the line cord and
played the D.A. for hours on end.  I occassionally checked the motor
for overheating.  One day I happened to feel the armored cable that
runs along the interior cross-beams and found it to be HOT.  I
dissected the cable only to find that the wire had a coating of green
gluck on it wherever it had been in contact with original rubber
insulation and was no longer a viable conductor.  My guess is that
sulfer in the rubber insulation reacted with copper wire to yield
something akin to copper sulfate, which is just about the color of the
green gluck.  Luckily the motor had sufficient current and did'nt burn
out.

   There is no question that old electrical parts must be refurbished
or replaced by someone with ADVANCED knowledge.  The way I see it, let
the added micro-switches become part of the instrument's history -- ke
a collector in another century will admire the handywork done to
protect the instrument.

  On the topic of applying wood filler, some books suggest a coating of
shellac BEFORE applying the filler.  I tried it, and it made scraping
the filler off a little easier.