I have dismantled the gear selector when the gear stick went “floppy” It is hard to get to and just fiddly. What usually prevents the gear shifting across the gate are the “springs” (pn 515891) not allowing movement of the two arms to engage into the correct slots. I ended up in restricting the spring movement using ty-wraps so they would not get bent out and restrict movement. Coupled with this, if there is anything not set up with the gear change rods and tower etc gear changing will be fun or impossible. 🙂
It is a matter of playing with each element logically until you achieve a smooth gear change…easier said than done!
By the way, if the gear stick goes floppy then the pin that holds it has sheared and will all have to come out to replace it!