I have a 2013 A6. Rear driver side footwell is collecting significant amount of water. Dealer thinks it could be a plugged sunroof drain, but it doesn't seem to be correlated to rain. Best I can tell, problem seems to get worse on long drives with A/C running. Next recommended step from dealer is to start taking interior apart (remove headliner, etc.). Has anyone had a similar problem on the 2013 A6? I do notice that earlier A6 models seemed to have had similar problem, but it was on the passenger side rear footwell. Could anything related to earlier model on other side problems help troubleshoot my problems?