When an accordion goes out of tune, rust is often the issue.
When you look at the reeds, you might not see the rust because it is
often under the reed on the blued area, but the sound of a rusty
accordion is characteristic; a lot of the reeds dropped in pitch.
Chemicals like naval jelly or acid will totally ruin the reeds; rust has
to be removed manually without scratching the reed plate.
The reeds have to be taken out of the frames, and the valve flaps
removed. If wax is what was holding the reeds on the blocks, new wax has
to be poured using the correct amount of heat, not a "medicine dropper",
or pieces of wax applied with a soldering iron, but wax spoons and an
alcohol burner.
Then the reed valves are usually replaced with new ones, although it is possible to re-use leather valves if they are clean, by re-shaping them
when they have gotten bent. The "leathers" should not be put on with
contact cement, but only shellac glue. "Elmers" or other water-based
glue won't hold on leather or plastic.
Plastic (vinyl) reed valves, on the other hand should only be attached
with adhesive, such as (possibly) contact cement, of E6000 or similar.
Once I ordered some valve glue from an accordion parts supplier, and it
turned out to be "Liquid Nails" which will totally mess up your reed
plates. i had to try to restore an accordion where someone had attached
the leathers with that, and got it on the reeds near the rivet which
made the pitch go way sharp and it was a chore to get it off.
There is a lot more to be said about reed restoration technique, and no
one should probably try this without a more thorough understanding than
what I have explained here in this short post.

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)