I'd been H2O hunting on my Mk3 Valver for a little while and eventually traced it's path back as far as the front passenger toe board, from where the trail disappeared up behind dash. Tried various fixes myself but recently gave in and sent the car for some professional attention. The screen was removed revealing extensive corrosion in the surround and associated damage to the seals. So, much welding, grinding and painting later, plus a new screen... and I still don't know if the problem's cured because the bloody sun's come out! Still, I'm sure the opportunity for testing will arise sooner than not and I'll let you all know the outcome.
S.M.