On a 1994 Force Outboard used to drive a pontoon boat, we have lost either the forward or reverse gear. If we adjust the shift rod up we get the reverse gear, but no forward gear. If we adjust the shift rod down, we get a forward gear and no reverse. We encountered this problem when we drove the boat through some thick weeds. A friend thinks the problem is in the top end of the shift rod, calling for us to remove the powerhead to get to it. Any comments would be appreciated.