ES250/2 Gear selector drum

[Andy]

Hi and happy MZ riding to you all , the sun is beating down on us and the roads are dry .........however my 1972 ES250/2 has not seen the road for a couple of weeks due to very worn out crank seals .
I have stripped the motor and fitted new seals ( big thanks to Matt in Bristol for supplying parts and taking time to make sure the correct seal were sent .....seems they come in 7mm and 10mm thickness .
The job went well and I hoped to be out and about today however I cant get the correct setting for the gearbox selector drum .
My drum has a line on the outer edge just bellow the toothed gear , I expect it will have to be correctly positioned to allow for correct movement of the selectors .
I have tried a couple of times to get the position correct but the box seems to index poorly.
Any ideas would be gratefully received .