You can shim the crank end float with the engine in the bike easy enough. You need to set up a dial gauge to measure how much end float there is and then measure the shim you have and get a thicker shim to “correct” the end float back into tolerance. I had a nose which was worse when I pulled the clutch lever in indicated excess end float was causing the primary drive gears not to mesh cleanly. The MZ manual is easy enough to follow if you have access to the right tools to measure the end float and existing shim and to remove the clutch.
I’m not sure but believe a more consistent “gearbox noise” may be because the primary gear itself needs shimming but I haven’t done that job, my noise was resolved when I got the crank end float in tolerance.
If you haven’t got access to an MZ manual I could email an extract to cover shimming the end float
Hope that helps
Andy