Garry I don't know if this will help mate but on my 41 with the four speed, I can't get it in to 3rd or 4th on the upshift or into 3rd from 4th on the downshift unless I slightly lift the reverse lock lever while changing gear. The spring on the lever must be either weak or missing. Like I said I don't know if it will help but might at least be worth a try.

All the best

Bob