Knocking on wood as I type i'm still on my original 1992 trim cylinders! Merc and most vendors sell a overhaul kit to rebuild the trim cylinders. I've also overheard a few conversations that guys have taken their leaking rams to the nearest shop that deals with hydraulic repairs and have had them done there. They are a very simple principle but I cannot seem to find the correct tool to get them apart. I've looked and can't seem to find any vendors selling one or a Merc part number.
I would overhaul the rams and go from there.