From the xray forum:
There is no reason to be concerned before you drive or even build the car. The car has plenty of hours of track tests in different conditions. Martin Bayer even used the final specs car in real races including the Czech Championship which he won, so the reliability was tested and is proven.
Slipper clutch - if you have the slipper clutch set loose you do not need to worry, the wheels will slip and the pinion will not break. If you however tighten the slipper too much (and this is what happen to those who experienced problems) you will create a solid axle instead of slipper clutch, the wheels will not slip and something (pinion) will break. That is common on all buggies of other brands using slipper clutch in the market.
Shimming the diff - Very Important - do not ship the diff. As mentioned in other threads, the diff was designed by purpose with a small play. If you shim the diff you will eliminate the play. The diff will during operation get warm and expand and if there is no play the diff will not work properly. Therefore there should be NO shims used.
Satelitte gears - they are made by purpose from composite, they are lighter and have better dynamic performance. They are moulded from very special composite mixture and have very good reliability. The same gears from same special material are used in the T4 and NT1 gear diff and the traction on foam tires on asphalt is several times higher than on a buggy track. Since there are no problems with the NT1 gear diffs at all there is absolutely no need for any worry about the composite gears for XB4. However if you want to feel more safe you can use the NT1 metalic optional gears #335030, they are direct fit.