I purchased a 2000 150 h.p. that has been sitting for 5 years, while changing the water pump I noticed the spline wasnt able to be moved, although it can rotate with pressure.The motor does shift into reverse but not forward, and the boat is on land.A mechanic said it may need water pressure to shift into forward, Im not sure why. What would cause the spline to stick, would soaking it in liquid wrench help?Any advice would be appreciated.