Hi Bob & TrF
It's alright they all do that. The problem is the phospher bronze bush in the cover it wears out, what do you expect after 30 years
Replacing the cover won't do any good as there will be a ridge worn into the shifter shaft that will, almost instantly wear out the new bush. The top lever that attaches to the main shift shaft, the one that runs through the engine will also be worn. It should have flat sides and round ends but they tend to go oval which means you need to throw the shift lever further to get it into gear. This, in combination with the worn bush accelerates the wear in all the other components, including the bush in the crankcase.
The only current solution is to replace all the components behind the cover, and the cover but I am currently working on a replacement cover that will be fitted with a needle roller bearing. This 'should' mean that just replacing the cover will solve the problem, although I always recommend you replace the top lever aswell.
New cover should be ready soon and after extensive testing will be available for sale through my website, all the other parts are in stock.
Cheers
John
www.tytrials.com
0845 108 1167