2006 Audi A6 - strange brake light problem.

[Vic]

I thought that after 40 years of owning Audis I must have experienced every possible problem that they could throw my way. Guess I was wrong.
Car is a 2006 A6 3.2 V6 Quattro. Problem started a couple of weeks ago. Every morning when I walked out to my garage I found the car's brake lights were on. They definitely weren't on the previous evenings when I parked the car. Depressing and releasing the brake pedal turned them off.  Figured that the problem may have been caused by the particularly cold weather we were having - and the problem did disappear last week when things warmed up. Unfortunately it reappeared this morning and it wasn't particularly cold.
Anyone ever experienced this bug? Only thing I can think to do is replace the brake light switch.

Thanks

Vic Norman