On our way to the Abacos (Green Turtle Club) the autopilot had trouble holding a course. If I engaged it on Nav to waypoint it would not hold a course. If I switched it to a heading (auto) it would hold a better course but still not good like normal. It had worked fine from north FL down to Ft Pierce but the crossing is where the problem started. I checked power steering fluid and pressure and fluid was fine pressure a little low at 10psi so pumped it up to 25psi. What would you check next?