[ddmckee54]

For a hydraulic piston just use a store-bought o-ring. From Ebay, Amazon, Aliexpress, or the dozens of other sites they can be had for about a dime a dozen if you look around. It isn't worth the hassle of trying to fabri-cobble a custom o-ring.

That stuff has its' uses, but this really isn't one of them. I used the high temp stuff from NAPA, in a 3D printed mold, to make a silicone boot for my 3D printer hot block. Still using it over a year later, it's probably got a couple hundred hours of use on it by now.