leveling jack stuck

I'm not sure I understand how pitting on the cylinder would cause the cylinder to stick. It would leak but I don't know that it would refuse to move. Is the cylinder stuck down, or is it stuck in the up position? Have you been able to move it since staying by the ocean?

Depending on the brand and type of cylinder, it may be repairable. However some cylinders are not designed to be rebuilt and are welded together. Rebuilding one like that is difficult if not virtually impossible to do.

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.

If you can free it up, spray fluid film on it, great stuff.

I had to replace one of my HWH jack cylinders and it was closer to $100 than to $1000.
bumpy

For anything hydraulic, I would talk to a person that deals with hydraulic problems not and RV shop. Not down playing RV shops the good ones are great, but an hydraulic expert may give you a better answer.

I have on jack that is slow to retract. At first I had to almost hammer it up. Then I thought why not use some dry spray lube on the exposed part. Since then about every other time I spray each part with spray lube and have had no problem.