I have a screw loose.  Well, not me personally, but my Duo-Art grand,
circa 1926.  There is a tiny screw with a collar that connects the arm
from the accordions to the knife valve arm.  There is also a small,
round, felt bushing that sits between the two metal components.

This little screw has had a tendency to loosen and come off entirely.
It is a royal pain in the you-know-what to put it back in because you
cannot get a screwdriver in there, the bushing falls all over the
place, one can barely see, etc. etc.  Been there???  The only other
option is to pull the expression box which is even more of a pain.

I thought about putting a drop of clear nail polish on the screw
threads, but even if I could get a brush up there accurately, I fear
accidentally getting the screw glued to the arm, which needs to ride
freely on the screw collar.  I'm hoping for a simple answer that
I am perhaps overlooking.  (Is there even a simple answer here?)

Thanks everyone!

Adam Aceto