Normally, on all racing bikes, the mainshaft slides easily out of the bearing holder
though I have dismantled a few nsr250 gearboxes for inspection and all of them had the mainshaft stuck.
Renewing the bearings didn't helped, #800 wet & dry sandpaper didn't helped as well.

I suspect that lack of lubrication and poorly maintenance e.g worn bearings, lead them to this condition though I can't really tell for sure.
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