I had the same problem and it was causing many DNFs, particularly on tracks requiring heavy braking.
I changed to the losi nuts, but this didn't solve it.
in the end, I resorted to threadlocking the nut onto the shaft - if done correctly, this 'thickens' up the thread on the outdrive, creating more friction between the nut and the shaft.
this techical solution was bought to you in association with 'carry on doctor'
