Switching problems 5-speed audio v8

Good morning forum,

I have the following problem :

I often have no "spring" resistance if I want to switch from the middle lane either to the 1.2 or 5. If I don't have this resistance, I'll end up in three or four.

If I just wait a bit (1-2 sec: so switch slowly and carefully) before I want to insert the next gear, or if I notice that the resistance is not there, back into the middle position and then press again to 1.2 or 5, then this springing resistance is back and I can insert the gear.

Which part is responsible for this ?
Is this a problem on the gears or in the gears?
If it's in the gearbox, can I fix it myself?

Thanks for the info.

Yours sincerely,
Stephan Rieke