Looks like you need to replace the output shaft oil seal. It is not a hard job and can be done with engine in place - at least that is how I did mine
My bike runs with no gaiter so do not worry about that. Just unbolt the shaft from the output shaft , slide it out of the way , prise out the old seal and gently tap in the new. Re-assembly is a reversal of above.
If you just use inner tube and glue you would allow the swing arm , where the drive shaft fits in , to fill with engine oil. Consequently the engine would run a bit low on oil and could possibly seize. Best case would be the diff unit would piss out oil all over the rear end of bike ( not a good idea )