I just had my 3pt apart for a different reason so it's fresh in my mind. It took me 30 minutes to fix the problem and about 4 hours to remove things to get at it. It's easy to change the seals once you get access to the cylinder, but depending on how your tractor goes together it could be quite a project to get at it. I would check all the linkages really well before you take things apart. My neighbor's JD had a similar problem and it turned out to be the connection point between the 3pt lever and the rod for the control valve that operates the 3pt. The lever was not really turning the rod but there was enough friction that it kind of moved it. Didn't cost him anything to fix it because the parts that fell off were laying on the sheet metal under the seat. Hopefully your fix is as easy.