MZ/MuZ Riders

Hi thanks for the add. New to MZ bikes and have been given the challenge of repairing a 1985 ts125 with only 2 miles on the clock....yes you read that right....2miles!
Basically my 2 issues are oil leaks obviously from the gearbox but can these seals be changed externally of has the box got to be split....found conflicting information.
Also gears from 3 upward down seem to have drive....any ideas there?
Any advice welcome. Thanks in advance

Also gears from 3 upward down seem to have drive....any ideas there?

not under standing the question but English is difficult to under stand even when its the only one you or i speak

after setting may be that the clutch plates are stuck together
or the oil in the trans is now goo
letting a bike set is most often harder on a bike then running the crap out of it

Sorry podgy fingers typing on the phone....gears from 3rd upward dont seem to have drive so gooed up clutch plates may be the answer. Looks like someone may have recently changed the oil just to make it look better and hoped it would solve it.
And ideas on the accessibility of gearbox oil seals?