Boscoe, thank you for your response.
It is multiple ram (pic attached).
There is no separate reservoir.
I have tried bleeding the system by raising the motor, removing 18mm bolt from right side ram, topping up fluid until overflow, replace bolt and lower motor, all using remote control button. Repeated this a few times with no sign of air coming out of the system.
When bleeding, the Engine only comes down until it touches the two short (trim) rams as they will not retract.
If I try bleeding again will the travel between the rams and fully up position be sufficient to bleed air from the system?
Small rams are not seized as they retract immediately when the by-pass screw is opened.
The Tilt/Trim motor sounds like it is still working when the motor reaches the rams. I was thinking about looking at new brushes for the trim motor but need to open it to check first.
There are no visible oil leaks externally on the rams.