Audi Stafford have messed up my car

[tonupkid]

Took the S8 into Audi Stafford yesterday for a service, MOT and new brake fluid.

They failed the cars MOT because it required the front number plate replacing and one of the read number plates was out... so they say.
The front number plate I can understand, but the rear light. It was working.
The sent me a video of it, with the bulb holder out, and as they moved it about it went on and off. Well those kind of bulb holders will do that if you wiggle them around.
The thing is, one of the screws holding the bulb holder lens in place had broken. A common fault. Therefore the thing was held with one screw and not perfectly flush. They suggested I fork out over £300 to replace the entire component onto which both the number plate lights are mounted. Without me having this job done they said they could not pass the car.

Anyway. I declined, took the car away and checking it over today noted that both number plate bulbs were working, and took it to a local garage for re test (MOT), as Stafford Audi is to far away.
My car failed the re test. Reason..... brake fluid squirting out of the NSF bleed nipple. How how has that happened. The tester attempted nipping it up, but it was apparent the the thread has been crossed. I drove home with care. Still no MOT.

I now have to get Audi Stafford to resolve this, after all it was yesterday that they replaced the brake fluid. I am concerned that the caliper may have been damaged. Is this likely with the nipple thread having been crossed?