What is causing water ingress in my 2008 Skoda Octavia?

I have a 2008 Skoda Octavia 2.0 FSI Tiptronic L&K estate, which is a lovely car marred by a persistent problem of water ingress affecting the rear offside passenger floor. So far, it has cost £320, part-subsidised by my local dealer, to re-seal behind the door trims and, when that didn't work, replace the rubber gaiter that protects cabling running between the body pillar and rear door. I understand that water ingress at various points is a known Octavia problem and wondered if you had any thoughts about this particular instance. Could pipework associated with either the air conditioning, or rear window washer, have anything to do with it?

Asked on 9 February 2013 by CM, Cambridge

Answered by Honest John
Most likely to be water coming in because the plastic damp-proof membrane between the door skin and the door trim has perforated. It's a common problem with VAG cars as they get older. Alternatively the pipe to the rear screen washer is leaking.
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