Had no problems with mine as yet, did put in the alloy gear and that just seemed to make the gearbox noisy (like a cheap toy car!) so put the std plastic gear back in and its fine! and I've run my XPro at 2 rounds of the Ardent winter series and a few club night
BTW I'm running a 10.5 motor (23 or 24t pinion) with a Tekin speedo (with boost and timing turned way up!! lol )