Drain the gear oil
Remove the 2 bolts which hold the propeller shaft housing in place
Pull out the propeller shaft & housing a couple of inches (Do this with the propeller shaft horizontal or pointing downwards & take care not to drop the clutch rod out of the prop shaft)
Drop the gearchange lever back into position
Re-fit the propeller shaft & housing, taking when tightening the bolts.
Test gear selection.
Re-fill the oil
The motor is 1990 (dark grey in colour with black & gold decals?)