98 uk turbo 2000

just wondering if anyone can help diagnose my gearbox probolem?
driving car the other day went to change from 3rd to 4th and ended up still in 3rd but gear lever moves about all over, just in process of removing gearbox (ty752vn6aa) thinking it may be a selector fork issue or does anyone have any other ideas cheers for any help

p.s. what are these gearboxes like to strip??!!