Parts to rebuild LH car brake booster

I posted a few months ago about my brake booster making a high-pitched
noise when the brake pedal is lightly pressed.

Based on comments here (and the fact that it is not getting any worse),
it is only a nuisance, not a real concern for brake failure. But the
noise is annoying.

Would I be right in saying that the source of the noise is most likely
in the booster valving mechanism, and more specifically, is a worn
o-ring? If that is a correct assumption, I'm thinking I could remove
the booster, disassemble the valve (remove one snap ring?), and replace
an o-ring or two that make up the sliding seals in the valve, and put it
back together to eliminate the problem.

(again assuming my assumptions so far are correct) Would standard buna-N
be the right o-ring material for the application (would Viton™ - or some
other material be better) - I assume it contacts metal (or plastic) and
air only - no fluids to worry about.

Even better, how would I go about locating a booster rebuilder (mail
order or local) that might be willing to sell an inexpensive rebuild kit
to me (I find no kits available in consumer aftermarket - only rebuilt
boosters)?

TIA!

Bill Putney
(to reply by e-mail, replace the last letter of the alphabet in my
address with "x")

 

Oh - not that it should make much difference, but this is for a '99
Concorde.

Bill Putney
(to reply by e-mail, replace the last letter of the alphabet in my
address with "x")