I found the hub nut came loose on my S2, after very careful examination we came to the conclusion that the Imp stubshaft was made of a mild steel which stretched & they were made to a price of zero, my machinist mate made a stub shaft & nut in EN24 (4340 US), end of problem, torque the heck out of it, doesn't slacken with 150bhp, an LSD & hillclimb slicks.