[Superman]

Yeah, I'd clean that up real good and finally use something like 0000 steel wool, at least, to try to get that bore smooth. Then I'd (of course) use a new rubber rebuild kit and I'd coat everything with Dow Corning 111 or 112 silicon grease. Especially that square-section o-ring that goes into the groove in the piston and rides against the bore.

You're doing the right things, Baz. Mechanical condition is important for aircraft in the same way it is important for motorcycles.