What's causing water to collect in my 1993 Audi 1.9TDI's rear passenger footwell?

I have a 1993 Audi 1.9TDI SE estate which I have had for 14 years. It's in very good condition and has done 104,500 miles. Three weeks ago I was emptying the car prior to taking it for its MOT and service, and I noticed in the nearside rear passenger's footwell a very large amount of water. I couldn't see where it was coming from so asked the garage to check it, so they put a hose on it but didn't have any success. I have since sat in the car whilst raining and put kitchen towel around the door and window frames, have checked the boot and spare wheel well but cannot see the problem. The car took in this water whilst stationary, on the drive. It is still happening and it is a lot of water.

Asked on 22 October 2010 by AB, Southend on Sea

Answered by Honest John
The reason will be a perforated membrane inside the door. These cars all have 'wet' doors. Rainwater flows down inside them and there is a plastic membrane between the door frame and the trim to stop it getting into the car. Over time these perish and crack. They cost about £20 each and you can DIY, but it's a fiddly job and you have to be careful not to break the door trim retaining clips.
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