One of the things that showed up on our first shakedown cruise concerns the single ram Imco steering assembly mounted to the outdrive. While going in a straight heading we noticed that the steering wheel position was changing and we had to correct it by turning the wheel to keep the boat going in a straight heading. After about 5 miles the wheel position went from a 12 o'clock position to a 6 o'clock position. Very strange to say the least.

sounds like fluid pressure is bleeding out of the steering ram, or possible air in the system

You will find that - particularly with a single ram system - there is no repeatable center position for the steering wheel. Every time you move the wheel, you open and close valves to allow the fluid to move. And every time those valves open and close, they let a different amount of fluid through. This leads to the "center position" changing. I have the same issue with the Latham Single Ram system on my outboard and I've just gotten used to it. Now if you didn't move the wheel at all while going straight, and the heading of the boat changed, you have a leak somewhere.

Is this a full, or add-on system?

The steering wheel and external single ram are IMCO. I am not sure about the hydraulic pump. There are hydraulic lines going to the front for the wheel if that helps.

If hyd lines go to the helm then its full hydraulic

I noticed this with my o/b hydraulic steering. Straight was never in the same spot of the steering wheel