Originally Posted by
FBinNY
Don't use proofhide. It's designed to penetrate and soften leather, and can lead to the breakdown of the piston.
You don't need anything special, and aren't trying to grease or soften the leather, just provide some lubrication where the leather slides against the cylinder.... I add one drop (no more) of olive oil (it's an Italian pump) and pump and spin the piston to spread it around the cylinder wall. That's good for a few years.
Natural (food) oils like olive and peanut oils contain acids hence their rancidity upon exposure to air. It it acid that breaks down leather??? Does Proofhide contain acids, too???
But I spread some regular olive oil from Wallys onto the leather washer for the first time ever since I've first purchased it in 2004. The washer wasn't dried out to begin with but I'll bet with the new application of oil, it'll provide a tad better seal.