I have tried using hot glue on roller organ pallets (and other metal
organette pallets) and sometimes it works, but other times they drop
off after a time, so something else is needed.  More recently I have
used a clear universal adhesive called UHU in the UK.  

Any adhesive which says it will stick to metal and felt should be okay,
including rubber cement.  Nearly all of these glues can be removed with
a good solvent such as acetone or cellulose thinner (just don't breath
while you do it).  I can't think of anything other than epoxies which
aren't likely to be reversible on a metal pallet.  Whatever you use,
use as little as possible.

However, I do wonder what they used originally -- perhaps shellac?
Does anyone know?  Is there a magic ingredient you can add to hot glue?

John Farmer, UK