Audi TT quattro rear differential damage

I own a Audi TT quattro. The car is six years old and have 48,000 miles on the clock. Recently I had the car serviced at a VW and Audi specialist workshop. Two days and approx 50 miles after the service I experienced a loud noise and loss of power whilst driving at speed on an A road. On inspection of the car by police and RAC the vehicle had suspected damage to the rear differential and was leaking oil. The car is now at the workshop that performed the service and I have been told the rear differential is cracked and needs replacement. I would like your opinion on what can cause such damage and how if the haldex oil change was performed incorrectly this damage can occur.
An over-tightened wrench not set to the correct torque when the plug was replaced. Specialist almost certainly liable.
Answered by Honest John on

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