window-sill of audi 100 typ 43: how to get into..

[robwill2 at wxs.nl]

Hi audifans,

Maybe any of you have the knowledge:
the right windowsill (vertical part) of my Audi 100 typ 43 
(1982) has a corrosion gap..
I want to weld in a patch of metal.
After that I would like to inject some rust-inhibiting 
material into the sill, but I don't find where the inside of 
the sill can be reached.. :-(
I assumed from the battery space side, but this doesn't 
seem to be so..
Probing from the rusthole side had no effect...

Any of you have a suggestion?
Robert