Rather than starting a new thread, I thought I would mention that I had the 16000 miles service done on my 2016 X yesterday and on checking the valves 3 were slack, 1 was a bit tight and the rest were OK. Seems good practice to get them checked as and when required.
Andy.
Hold on a minute! Have you proof of that? Have you had the oil analysed? Or is this just a personal theory expressed as a "fact"?
One thing that might cause clashy gearchanges is if the clutch is dragging - I'd check that.