[ Ref. 080812 MMDigest, "Seek Duo-Art Linkage Screws"

The subject of shoulder screw shims has been touched upon only
briefly.  Aeolian always used these to prevent rattling; they were
made of either pouch leather or cloth reinforced felt.

When leather is used, it should be saturated with neat's-foot oil
or a good machine oil to prevent whatever corrosive effect on the
metal that the leather may have.  Any excess oil should, of course,
be blotted away.

Jeffrey R. Wood