Not had to actually change any parts on the gear change but I would say any looseness or play needs attention of some sort. One problem that quite a few of us on here have experienced, including myself, is the circlip coming adrift and the mechanism falling off whilst riding. In my case half way round a tight bend when I needed another gear !!!. I just fitted a new circlip, I think Mike the Bike drilled a hole in the shaft and put a split pin or wire through it to stop it falling off again.