check the seals by all means but if this is a fluid displacement cylinder then there are no seals on the ram, they are all in the packing nut on top of the cylinder shell where the ram comes out.
You are going to have to remove the cap/packing nut anyway to get access to the inside of the freelift cylinder so once you do this remove the ram and look in the base of it and check the safety flow valve. Make sure it is there and intact, if it is not then it may have come apart and is laying down in the bottom of the cylinder in smashed up pieces.

I have see quite a few of these do the exact thing you speak of and pretty much always it was that safety valve causing a misstaging problem. Usually caused by the snap ring failing that holds the valve in.