I would start from finding out what lubricant Audi is using during longlife service (same probably as the standard service) on your locks and hinges.
I do a longlife service almost every year since day one, not because I have to, but because I'm stupid 
We all going through pretty much same winters and I never had issue with the lock.
So it could be a lubricant or certain batch of locks which cause this issues.
Lubricant is cheaper than lock so I would start from it
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2006 D3 S8 5.2 V10
Ceramic Brakes, Bang&Olufsen, DTV, DAB, Rear Camera, BT, TPMS, Soft Close, Auto Boot, AMI , 4 Zone AC, Home Link, All Electric Blinds, Fingerprint, Ski Hatch, Black Extended Leather, Heated Sport Seats, Alacantra, Carbon Trim inc Aluminium Pack 2.
2015 A3 S line 1.4 TFSI - for the missus to keep her away from my car.
Standard S-line equipment, no extras.
2006 D3 A8 3.7 V8 - SOLD but not forgotten
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