Can anyone please help with my gear selector shaft??

[Dannylewis27]

Hello, I have a 98 aprilia rs extrema 125.

Recently my gearbox decided to eat itself and am now having to change it

My new one arrived today but a few days back the actual gear selector shaft popped loose and I haven't even able to figure it out (also can't find any info on it online anywhere!)
I have a video here of how I reassembled it

If you turn the drum it clicks as it should
But if you turn the selector shaft...nothing happens, or it pops out of place

Can anyone please help me?
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Derbi senda R, 03
Aprilia RS 125 Extrema, 98

[Nope.]

Maybe if you posted in the correct section (The Workshop) rather then new bikers you might get more responses.
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Former: Derbi GP1 50, Sachs XTC 125, Suzuki GSXR 400 GK73A, Kawasaki ZX7R, Suzuki DR250, Yamaha RD350
Current: 2011 Yamaha XT660Z Ténéré, 2003 Yamaha YZR-R1 5PW (In Build), 2009 Kawasaki ZZR1400