[ainarssems]

The moisture gets in by the handbrake lever shaft in the caliper and start corroding, which introduces extra friction and the spring does not fully return the lever when handbrake is released, this means self adjusting mechanism in caliper is not working properly.

It's a design feature for the Audi's of that era. Was a problem on all I had with quattro, not sure if quattro are more affected as I never had front wheel drive long enough. If you spray some penetrating oil and exercise the lever it usually frees up enough and self adjusts inside caliper so that it passes MOT and is good enough till next year. Small amount of waterproof grease where the shaft enters calliper might help to seal it off and slow the moisture ingress.