When my boat had problems last summer, my mechanic told me that a coupler fails for one of two reasons, either excessive run time so its just worn out, or somthing is out of alignment. The alignment thing was what got me, resulting in the coupler failure. When you pull your motor, have the motor mounts, engine beds and stringers looked at carefully before you make any decisions, as the underlying factors that made your coupler fail need to be fixed as well, or your next coupler will fail again.