I have a little issue with a B4.2, in the ball diff. Running in 2WD stock, and the diff was coming loose, usually after only around a minute of running. Replaced the locking nut with a new one (#6575) however the result is still the same. Surface is regular, untreated dirt track, slipper set so slip can be heard for around 2 seconds on a full throttle launch.
Is it possible the diff needs to be fitted the other way around? I'm thinking it may be unwinding itself, though the manual does not appear to show anything in this regard. The way it is currently fitted, the adjustment screw is accessed from the right hand side.