Hey everyone. I have a 2004 Pontiac Bonneville GXP with a leather and suede interior. I noticed some moisture stains a few weeks ago on the rear seat where the bottom cushion and seat back join. I checked last week after we had a few days of rain and, sure enough, the whole back seat was wet. There is absolutely no water in the spare tire well, but the carpeting back there sometimes feels a bit damp but much less damp than the rear seat.

Any insight? Do I have bad trunk seals or is something else going on? Thanks in advance.

Do u have a sunroof? I never had never boonies but I had 2 mid 90' and I can tell u that those shitsu rust like ! I ask bout sunroof cause I heard sometime before that instead of fixing problems Gm made it worse! I heard those newer specially w sunroof will have water inside car and rust even faster, so be careful. It have to do w sunroof water drainage sleves, somehow a very stupid idiotic design or some like that. I'd take seats of and see if u can see ground through it or not and if it' not to late, Vaseline all that gets wet after u dry it of

Nope, no sunroof. I will be pulling my back seat up this weekend for my audio install.

Does the bottom of the seat pop out in the GXP like our Bonnevilles? If so, pop it out and see if there is any water underneath the seat. Does it look like it'* seeping through the crack in the seat out?

Honestly, the best thing to do is probably sit in the car and have someone go over it with a hose to see if you can spot where it is coming in at.

Yes, I believe the bottom pops off-- that'* where the battery is. I will check down there this weekend.

It does look like its coming from the 'crack' out. It comes out about an inch and a half on the seat bottom and goes the same distance up the seat back all of the way across the seat--all of which looks like it had an origin of where the seat back and seat bottom join.

Could be a long shot, but worth checking anyway.

Pop the trunk and pull the cardboard cover away from whatever wheelwell is on the side of the interior leak. Check for rust-through or a hole.

Rain, tire throws rain upward while driving, rain through the hole, water funneled behind seat into the interior, wet seat and floor.

Strange, but true. Good luck.

take out the bottom of the back seat and run your hand down the carpet to the floor. See if the underside of the floor carpet is wet. That will help tell you where to look next.

Have you had any window regulators replaced? If so, that may tell us where the water problem is originating.

No, I haven't had the regulators replaced-- but that'* not to say that the previous owner didn't.

The water leaks on 2000-2005 Bonnevilles' typically come from three places:
sunroof (clogged drain)
doors
trunk

We need to narrow it down.