Thanks Gregg,
I already replaced that, bought all new OEM seals and relief valve, full kit but didn't remove the issue with the leak down on pressure, BUT great news, I did some research based on your last post with the older info and it seems the old Tilt & Trim units like mine actually do work much more efficiently with ATF-A or equivalent, and the seals throughout need the older mineral based lubes to really be top performance. I've spent over 20hrs reading about the older tilt and trim units and luckily I got some info from a site in the states that advised backward compatible fluids. It said something like the old ATF-A fluids were made from Whale oil and "what's now classed as other endangered species" so it was stopped being used BUT they found another mineral replacement. The say the closest to it is ATF Dexron 2 as this is mineral, and they advised against Dexron 3 as that is synthetic, and they say the older units and the seals still out there for the older units, need the mineral based oils or they don't work well and the seals melt in no time.
I've drained the unit and replaced with ATF Dex 2 and it's totally different, the pressure is much higher and the ram is solid, and has been extended for 29 hours now with no pressure drop. It's not currently under full resistance so may compress in those conditions but the new fluid seems to have done the job. I'll definitely put this in the other second unit I have as a spare.
Thanks again to all the great folks for all your support, great support community on here>>>
Best
Mike.