I have this autopilot on our boat. The manual says to rinse the gears inside the wheel drive (the part that fits on the steering wheel) with water after every sail, but not to lubricate with anything. There is a plastic belt in there which has teeth which can wear/break off, so the belt may need replacement. You can take it apart by prying the two sides of the wheel drive apart with a large screwdriver (and it clips back together with pressure).
Unfortunately, the belt is very hard to find now, as they have replaced it with a new model. Even Raymarine wouldn't send me one--suggested I send the wheel drive in to them (in the US) and they would replace the belt with one of the few they had left (at a cost of several hundred dollars). When I asked them to simply send me one of their few left over belts, they refused to do that. I eventually found one at West Marine (there were only 3 left in all the West Marine stores in North America according to their computer inventory). It took me about 15 minutes to replace the belt--for which they wanted to charge me several hundred dollars!