Ferm, Chum And The Rest. . . . .

[spareparts]

If it hasn't allready been done, it may be time to replace the shift shaft in the lower unit, its not a hard job, you will need one special tool, but there are ways around that. If it has the original shift shaft, it may have corroded enough to allow slop in the splines, casuing you to not have enough travel to achieve proper shifting, there are several other reason for the shifting to be out, but this is a good place to start