I haven't replaced that yet, BUT I'm sure its similar to a steering cylinder in that there is a rubber seal inside the cylinder thru which the trim rod goes, and eventually your seal will wear enough to leak fluid. The bad thing is that w/ my steering cylinder I could add more fluid at the helm and it would be good for a week or so, but I don't know how to add fluid to the trim cylinder, so you may face a more immediate fix. Hopefully if it fails it will be in the down position.
But the seal replacement kit I got from Seastar Steering costs less than $100.
But the seal replacement kit I got from Seastar Steering costs less than $100.