Suggest that you call Rob at BlackDog Marine for Mercury/ Mariner spares 01503 265 898 (mention that you are on Ribnet too) - I have always had very good service from them.
Thinks I may have a used PTT system knocking around which may offer you the parts you need. It's one of a few that are sat in storage having been removed when faulty, yet to be looked at. I think one had it's motor removed for another unit, another had an issue with the hydraulic side of things, again not investigated. We tend do replace rather than repair then they sit around until time allows a look at them.
Both have no leaks though. what exactly is the problem with yours ? Do you have a pic of the unit ? I'll compare as I forget what one came from what engine
Any Source of repair/replacement would be a help ,I have attached aphoto of the unit on mine,
The outboard is virtually the same as the one you had for sale a couple of weeks ago (Ex Mod) ones.
It leaks from the top seal , and has to be refilled every 3/4 trips out otherwise I cannot raise the o/b to lock in position to transport it.
If the one you have is the same please feel free to pm me.
Im sure i do have a complete unit with that square PTT motor on it. I'd have to find out what it came in off etc but looks the same unit and without any leaks!
Ive had quite a few come in with faulty "scraper seals" and they are a pain in the A*** to get parts for. I did have a local hydraulic repair shop (non outboard) who would retro fit a larger seal (by digging away to create a better fit with a larger diameter seal) but I think they long since gone to the wall. Might be worth checking around though if you want to repair what you have. In my experience they don't last too long anyway though once repaired.
What is a complete unit worth to you working ? What's it worth in parts and what would you require ? The problem with that is I'd rather not break a unit which renders the remains pointless but then if I check and find it's faulty (ie motor etc) I could maybe split it up anyway
Here's the one I have - no idea which motor it came off I guess a mid 90's 75hp
The motor is good so I'll remove that and keep it incase I need it ad there's mo point you paying more when you don't need it. The rest is advised as unserviceable on the basis that the pump has suspected to have failed.
The part you need being the seal end cap is fine and without any leaks. Weather you can simply swap the caps or the entire cylinder etc I don't know. yours looks cleaner though!
The diameter of the actual ram is 17.37mm.
I'm happy to sell the entire kit (minus the motor) for the cost you said you were quoted just to repair what you have -£75 + pp, which gives you additional spares should you need them.
, If you find one please post a link, 
