Protective caps for plastic differential bushings are fitted using a locking plate and special bolts with a fixed washer.
It's not a good idea to reuse the old plates, as they not only fix the caps with a larger surface area than a normal washer, preventing them from cracking, but also act as a locking plate.
If the bolts have been loosened using the wrong size Phillips screwdriver, there's a good chance that the head has been broken off and therefore can't be tightened properly.
These are not standard bolts; they have a specific size and hardness. Therefore, do not replace them with other bolts, but only with bolts that comply with Volkswagen specifications, such as those listed here.
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