Lester Hawksby writes, "I would really appreciate any advice on
which is best -- wood filler, burnt shellac, dowels, veneer,
patches of rubber cloth, or the much more laborious matter of making
grain-aligned plugs?  For that matter, is any approach proven
disastrous?"

I'd suggest that the only method that is not potentially disastrous
-- and certainly the only one that leaves a permanent, professional
looking repair that will hold fasteners like new wood -- is the
cross-grain plug.  I'd also strongly argue that it's not significantly
harder than the other methods mentioned, so why not do it right!

Tapered plug cutters are widely available from any woodworking store
(Woodcraft, Lee Valley, Rockler, etc.; it's worth buying a good one
rather than the Harbor Freight specials).

You can make a large supply of plugs in a short time from the different
wood species you commonly encounter.  Take a board and make rows of
cuts with the plug cutter at the drill press, then set it on edge and
run it through the bandsaw to liberate all of the plugs in one pass.

To fill a hole, use a brad point bit (to avoid tear out) to drill
a hole centered on the screw hole that matches your plug size, drill
to about the depth of your plug, apply either hot glue or yellow
carpenters glue to the plug and hole, then pound it in nearly flush,
matching the grain direction to make it less visible.

You can, but you don't have to, wait for the glue to dry to trim it
flush; typically a swipe or two with a block plane does it.  This whole
process takes about a minute and doesn't leave your instrument looking
like a hack job.

Roger Wiegand
Wayland, Massachusetts