After rain, noticing some water on the upper right-hand corner of the front passenger footbed (LHD car). Thoughts on where it could be getting in? I have checked the weird rubber drains on the firewall in the engine bay (the round caps were plugged but disintegrated when I touched them so should not be preventing waterflow now). Also checked the recessed area under the wipers (underneath that screen thing), as well as up by the sunroof, where there appear to be drain holes. No obvious blockages, although it's possible the sunroof holes are plugged further down I suppose - is there a way to open those up for better access?

Any thoughts appreciated. I am getting some proper floor mats so hoping to get it cleared up and dryed up before installing!

 

The most likely cause is corrosion around the windscreen - do you see any paint blisters at the bottom corners or anywhere along the bottom of the windscreen stainless/rubber trim? If you do, and the chances are that you will, please note:
The rubber strips on both sides of the stainless steel trim is NOT a seal. On the Series III cars rust forms in the bottom channel because the rubber actually traps water there - and the eventual result is holes in the channel allowing water into the cabin.

The front sunroof drains/hoses empty directly into the fender (behind the leaper badge). That is unlikely to be the cause of water ingress.

 

Aha- yes they makes sense…have some bubbling at the bottom of the windscreen, right over the passenger footwell…

thank you!

 

Is the Series III windscreen held in the same way as the Series I? I found this DIY video on a Series I windscreen removal, and am thinking about trying it myself.

What kind of rust damage causes the leak? Is it actually holes in the channel? So maybe sand, scrape, and Bondo?

 

I had a similar issue and found the leak to originate from the fresh air intake box in front of the wind screen and below the chrome grill between the wipers. There are two drains in that box that exit under the car on either side of the transmission tunel. You will have to get the car up on ramps and crawl under to find them, about half inch rubber hoses. I cleared mine with a stiff but flexible wire and about a liter of water came gushing out. It may be easier to remove the chrome grill and probe the drains from above. Water accumulation in the air box can get into the interior air distribution ducting and leak out into the foot wells.

Bart
'86 Vanden Plas

 

No, the windscreen is not fitted the same way as in the earlier cars. It is bonded to the body with adhesive. The metal and rubber trim is just that, trim. But water gets under this trim and tends to stay…the eventual result is rust, yes, rust holes in the channel. The proper fix is to remove the trim, remove the glass, clean rust away and put new metal in where there are holes. Repaint that section, refit the metal and rubber.

Bondo is a temporary cosmetic fix. The rust will reappear quickly if the channel is not properly repaired.