[lincpimp]

I am sure the main issue is caused by the slack that exists between the sliding coupler and the output gears. When you use the brakes the motor stops, as do all of the gears in the tranny. The coupler can rotate as much as 60 degrees before it engages the output gear. This shocks the gear train in the tranny and that weak roll pin takes a hit. After time this will eventually break it. Also with high power brushless and grippy tires the roll pin is simply the weakest part, especially if you have the slipper set tight.