Different application, but I had a hydraulic leveler on a flatbed trailer that had pitting and rust with the rust buildup preventing retraction of the male part of the cylinder.
It was stuck in the extended position, so I could get at about 80% of the length to hit it with a wire wheel and lube. It was a good fix, but the "barrier was breached" and I had to repeat the cleanup about every 4 months or so...in the end I replaced it, but that jack only cost about $500 and 3 hours of my time to replace.
I'd think if your jack is stuck in the extended position, sanding and lubrication will solve the immediate problem, but only on a temporary basis.
CRL
My RV is a 1946 PA-12
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