It's mad that the thickness of a gasket is enough to cause problems engaging gears 🤔
Not unique to Beesa 'boxes GB, sadly. Folk find Burmans can be a very regular source of similar angst, and there be others I think. All down to wear, small amounts, multiple places is what I have found over the years.
I remember my old Dad saying to me one time about 50 years back "Don't even GO there, you
stupid boy, that's GEARBOX, it'll be Trouble, Guaranteed, you'll see!"(Which, translated, actually meant: 'Leave that to me" - so things always ended happily and I learnt stuff.)