G50 experts? Grinding problem

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I have some problems with my G50 gearbox.
When I engage 4th gear it grinds a little, not grinding that in worn syncros, 4th slips in fine but when you pull the lever there is no "dead zone" after it goes into gear, it grinds. So if you are careful you can shift into 4th, but that's difficult.

I opened up the gearbox today to see if I could find anything and I think I did.
I'm not sure of the correct terminology of the different parts here, but here it goes..
It looks like the teeth on the slider for 3rd and 4th gear can be pushed to far down so the teethes touches the gear on the output shaft.









I can't see any way to prevent this, I can't determine any way to adjust it.

Does anyone know of a way to fix this?