I'm guessing this is because of bleeding problems and the rear brake going soft?
I swear it's a design fault with the underslung rear caliper. The rear brake on the 600ss is exactly the same setup, but the caliper sits above the rear axle - and it doesn't go soft! Dunno how easy it would be to change it though...
BTW, have you still got the m/c mounting bracket I lent you ages ago?
