There is a modification kit from the factory. The part number has been mentioned in an old forum topic, cant remember which one. Only the better dealers actually read and save the service bulletins in which these things are announced, so it could be that your local dealer hasnt heard about it.
When we bought a 5245 in 1999, it double shifted every time, so we went back to the dealer and helped taking the transmission cover off, serviceman welded this guide plate on top, an that was that, it never happened again.
On older models i weld the wear grooves in the selector slide slots just as a precaution, when its open anyways.