[ralphhughes]

I think you may be onto something here. Taking apart old machinery I have often observed that the hardened part of a shaft is worn and has a noticable groove detectable with a fingernail. However the part that rubbed on it is often much, much softer eg a rubber oil seal. My theory is that the much softer material is so soft that microscopic inclusions of something much harder (grit?) are caught in the material and then abrade the harder shaft. Something similar may be occurring in the keys on glass case?

[drjasonharrison]

Cutting with a lubricant and grit is super effective. Silicon dioxide, that is sand, is everywhere.