It would be worth a try. However, I suspect that the wd40 would not penetrate past the outer edge of the piston, which would leave the 5200 between the piston and the cartridge wall to set up and lock the piston. OTOH if wd40 is really, really good at repelling water, perhaps it would actually prevent vapor from getting in there, in which case it might prevent the piston from seizing.

Best regards, Allan Edie

: Perhaps a quick shot of WD40 into the plunger end would work?