Wow is this a common issue ?? cause mine is doing it too, every time it rains hard when it sits in the driveway i go out and the ps floor is filled with water, so i just vaccum it out.

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SLP headers, Wizaird cai, zzp1.0pcm ,slp powerflo catback,
3.4mps, al 104's, 180*, zzp stage 1 hv tb, flipped motor mounts, spring blockers And much more to come!

Very common. I'd say 8 out of every 10 W-bodies that I replace the windshield in has this rubber seal under the cowl at least partially displaced.

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NGA Master Certified Auto Glass Technician
Kansas City Pontiac Motorsports Club
My F-Quick Garage
My GPF Garage

a common issue is a blocked drain just shoot some pressurized air in the driain

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RIDES: 99 DARK BRONZEMIST METALLIC GTP SUPERCHARGED SEDAN. -MODS- CUSTOM FWI, CUSTOM GRILLES PERFORMANCE PLUGS, ENKEI stock RIMS, RAISED SPOILER, KENWOOD SOUND SYSTEM. RED CALIPERS AND ROTORS WELDED THURSH DUAL EXHAUST

Just fixed mine, sure enough it was off. I did it without removing the wipers; I just turned the car on so the wipers were straight "up." I shut the car down and maneuvered the cowl (one piece) enough so i could pull off the deflector, put on RTV and reattach the deflector. I tried to take the wipers off but they would barely budge. When I was finished, I just turned the wipers off and let them set in the down position, and whacked them a time or two with a mallet and tightened the bolts down. I don't remember removing the wipers when I had to do the same thing on my Impala, either.

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2004 Impala SS - ZZP PCM, 3.4" Pulley, K&N CAI, TOG Headers, SLP Cat-Back, 180* thermo, Autolite 605s, PRJ Performance wires, Alternator rewire, GMPP Handling kit
2000 Grand Prix GT, Commuter Car - K&N CAI, GMPP Handling kit, ZZP downpipe w/U-bend delete, ZZP Plog, Alternator rewire

GLAD U FIXED HER MAN soz for caps

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RIDES: 99 DARK BRONZEMIST METALLIC GTP SUPERCHARGED SEDAN. -MODS- CUSTOM FWI, CUSTOM GRILLES PERFORMANCE PLUGS, ENKEI stock RIMS, RAISED SPOILER, KENWOOD SOUND SYSTEM. RED CALIPERS AND ROTORS WELDED THURSH DUAL EXHAUST

I realized WHY I didn't remove the wipers on my Impala. If you put the wipers in the up position and have a two piece cowel, you DO NOT have to remove the wipers. Whoever updates the How-to might want to add this.

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2004 Impala SS - ZZP PCM, 3.4" Pulley, K&N CAI, TOG Headers, SLP Cat-Back, 180* thermo, Autolite 605s, PRJ Performance wires, Alternator rewire, GMPP Handling kit
2000 Grand Prix GT, Commuter Car - K&N CAI, GMPP Handling kit, ZZP downpipe w/U-bend delete, ZZP Plog, Alternator rewire

Is this just a GM issue in general?

This post was for GP's up to 2003, but mine is a 2004 and I am experiencing the same issue. I actually just made an appointment with the dealer to have this looked at, but tomorrow I might try to do that on my own.

THIS THING JUST LOVES TO LEAK THOUGH...

My Onstar Antenna leaks as well... comes down through the overhead console and fills my cup holders.

This happened also to a Grand Am I used to drive, as well as a friends Impala.

I can't remember off the top of my head if the '04's have the same seal. I know they have a similar cowl design. The directions here are for up to '03, so you might have to just use it as a guide as some things may not be 100% the same.

The OnStar antenna on the roof is also a very common problem. A friend of mine had the same problem and the dealer just replaced the antenna and it fixed the leak.

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NGA Master Certified Auto Glass Technician
Kansas City Pontiac Motorsports Club
My F-Quick Garage
My GPF Garage

Yep, sure enough...

I went out and the 04's do indeed have that same disastrous design... Even better, mine does have cabin filter installed from factory... SOOO I better replace that ASAP because I'm sure it will be full of mold/mildew if it isn't already.

And of course, there it was just sitting there out of place....