Ride Height Sensor Design Guaranteed To Fail

[kccmc]

2015 Q5 TDI Premium Plus level sensor on left rear suspension failed, causing headlights to be pointed downward and not safely lighting the road ahead. The sensor failed due to poor design, metal-to-metal ball and socket linkage in a corrosion-assured location under the car. When the metal-to-metal ball and socket corroded and froze, resulting load caused the sensor linkage to break. A search of Audi forums indicates that this problem is not uncommon, and this same sensor design is used in other Audi models and variants. This should be a recall item.
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[camouflage]

It is not metal on metal but a metal ball in a plastic socket. The metal ball corrodes due to trapped water and then expands with rust and freezes the joint.
There are some great DIY write-ups on how to replace this arm with sealed rose joints as you can't buy just the arm on its own. Good luck with the fix!