The water runs down the firewall and under the sound deadening material to the back floorpan where it collects (this is the lowest part of the floorpan).

Unfortunately, extra drain holes will keep the space between the floorpan and sound deadening wet, and this will rust out the floor eventually.

I'd replace both windsheild gaskets when I had a chance -- if the rubber that contacts the body isn't flexible, the gasket is shot. Water will leak in over the seal lip and run under the sound deadening material and into the trunk, causing lots of rust.

Don't use any sealant -- the gasket will take a while (a week or two ) to completely conform and seal, and all the sealants I've seen set up too fast. This results in a windshield that leaks from the day of installation, even with a new gasket.

Replacing the gasket isn't a big job, unless you have to repair the paint underneath first -- the paint must be intact and prefectly shiny, or it will leak.....

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!