Similar problem but fortunately not lethal. Found this on engine undertray on A6

Is that a relay roller?

Half or should I say third of AC compressor pulley/clutch. Bolt have become undone and was missing. Main part of the pulley and the belt was still on. Wife complained that AC was not working couple of weeks ago, I did all the electrical tests and they were fine, thought maybe belt was gone but did not look at it as I was going to service soon car soon (today) and left it as it is until now. When removed undertray to do oil change there it was. New M6 bolt, washer, threadlock and couple of minutes later we have working AC again.

All did not go so smoothly, it's pain in ass to bleed fuel system on diesel after filter change without proper vacuum pump. I thought my lips are going to be blue/black from suction by mouth with my homemade bleeding kit from 2 liter bottle and a bit of hose but I got there at the end.

Also Eurocarparts sent me wrong brake discs. I ordered 312mm with 112mm PCD, they sent me 280mm with 100mm PCD(Golf/A3 maybe). Part number on the box is correct but contents wrong. I painted areas that does not come in contact with pads with heat resistant aluminum paint before checking so can't return either.

Also found that tracking rod ball joint has a play on one side. I do have a spare pair but old one didn't want come off even with a lot of banging, WD40, Freeze&Release and other similar stuff. I have been up since 3am so gave up and will do attack with blowtorch on round 2 when I get correct size brake discs.