I have been experiencing difficulty in getting my boat to change gears from reverse to forward when backing out of the marina berth. The gearbox has been out and there is an obvious difference in the reverse operational characteristics and forward but if I reduce the revs very low the gearbox appears to operate. "Sometimes" but it usually decided not to operate in the most awkward situations. Once the gear has been selected I can motor all day in forward without any apparent issues. Has anybody experienced this issue? Is the fact that I have never changed the oil in the gearbox, only topping up an issue? Has anybody changed the forward pressure plate in the gearbox to overcome similar problems?