The standard Li, SX gear selector arm system can be considered a weakness in the gear change system.
The arm works loose on the shaft causing imprecise gear changes and the tiny circlip can fall off, leaving you stranded unable to change gear.
The GP type arm is an improvement but still depends on that tiny circlip.
This MB made arm is modified not to use the circlip comes with a stud, washer and nyloc nut.

HANDY HINT - When fitting this item set the selector to 2nd gear then fit the arm so that the external arm is around 90 degrees to the crankcase side gasket face.
This will ensure that the gears will be in the correct position when all the cables are connected properly.

TIP - grease the stud before fitting the tie bar, fit the plain washer then the nyloc nut, tighten the nut tight then undo 1/8 of the turn so the tie bar can move.