For those of you who say "always replace" - ignore the following.
It is for people like me who find it pointless replacing with weaker modern
replacements unless the original is obviously weak with much reduced
switch-closure force.

Yet another amp "failing" due to dirty/grimey such unused bypass switch.
I prefer to beef up the closure force on the existing ones , after cleaning
the "contacts", (contact is far too grandiose). The spring action is still
good but beefing up will make dirtying/griming of contacts less problematic,
loss of amp-preamp by-pass action less likely, better contact with 1/4 plugs
where the send/returns are used.
Requirements - Hama beads (small
coloured plastic rings, trade name, they get everywhere if kids use them)
for making pseudo mosaics on a sort of pegboard found in toy / craft shops,
the size required here 5mm wide, 5mm outside diameter, 2mm inside diameter.
2mm silicon rubber cordage from angling shop.

Two plastic beads rest neatly in the exposed groove part of the flexing part
of the switch, to spread load , locate neatly in housing and act as grips
during assembly. Take 2 beads and 150 mm of cordage , pass through both
beads and return to pass through a second time. Pull the first cord to
reduce the diameter, introduce the other cut end and by a "preristaltic"
action pull the second run through each bead like this. Pull tight to form a
loop of about 6mm diameter. 2 tight passes through 2 rings mean this loop
stays as formed while finishing off. This loop, stretch over the open end of
the socket, with the beads in the groove. Loop the free ends of the cord
around the other side of the terminals and wires and tie tightly via the
other side of the terminals at the "hinged" end. Swathe in hot-melt glue to
avoid the knot untying and bond to the socket housing, to avoid the hinge
end , free end of the socket , cordage dropping off again, unlikely as the
contact ends drop in a slot in the housing . Cut off loos ends of cordage.

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/