Sorry to hear. These bolts are supposed to be use once only so you need to replace them every time you undo them. I have seen them come loose on many VAG cars if not replaced. They are either different tread angle for bolt and nut(60&55 degree) or pre-coated with thread-lock so that they do not come loose easily. In my personal experience I never replaced them but always used thread-lock to prevent them coming out and never had any issues.
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Currently 8less
2011 Q7 S Line 3.0TDI, 2016 Tesla Model S 90D
8 history:
2006 A8 Sport 4.2TDI quattro SOLD,
1997 S8, reached end of life with gearbox failure
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