Hi Sam

I've had 7 NSR's all SP/SE's and only one (an MC28) had a dodgy gearbox - in that it jumped out of 4th. So generally they are very good. If a bike is breaking several gearboxes, then it might be more to do with his riding or how he puts the motor together.

I don't think there is a kit gearbox for the NSR - it's just a myth (see Tyga website for their Q&As and ratios), the MC21 and MC28 have slightly different ratios in 4/5/6, but the 'kit' mod was to use a 21 gear box in the 28. You can I believe get a different gearbox for the F3 model, but that requires F3 crankcases - rocking horse do do and mega £££s.

Cheers

Dan