It's hard to believe that most of these trucks are now pushing 20 years old now. It's less about the design/engineering, though they could have done better in a lot of areas., at this point and more about the maintenance due to age and mileage.

I've learned over the years GM did not have both eyes on the H2 when it came to the H2. Keep in mind they shared engineering, design, QA, and production with AM General. A lot of what we see in terms of bad, and good, design decisions was due to this partnership in the creation of the H2.

 

I know this thread is old but it helped me in the past with various leaks in my H2 over the years. It was always the grommet in the markers or the top outer seal getting dirt filled as described in this thread. The last one had me though. No matter what I did there was a steady flow coming in behind the panels and ending up under the drivers side floor and running to the back. Wet wires and shorts, dead battery, the works. The second body shop I took it to found the leak. Turns out it is the roof and side panels of the truck which the seam for these three parts meet at the gutter just behind the roof rack rails. It extends the length of the H2 front to back. The GM body sealant is prone to crack with age allowing water to leak in. As stated, these trucks are now going on or over 20. So I hope this helps someone.



As an interesting side story, when I was a teenager working for my Dad’s canvas business I had the opportunity to work with the engineers at the GM plant, I believe it was in Linden NJ (if my memory serves me). The very first prototype H2 Hummer actually had a canvas soft top. It was a dark tan body with a white, vinyl (Chrysler top material). It was such a cool design for its time. The truck would show up locally in parades from time to time I was told. I don’t know what ever became of it or any other prototypes that may have been built after that one.

 

Try $70 grand for the first Victory Red H3 with the military bike, yippee !, that leaks and has ruined the head liner, the driver side carpet only in one square is a puddle like a swimming pool, good job GM !, and I'm still chasing the leaks to no avail,

 

i am so glad you added this info, i am going to try to figure out where on the hummer your talking about, but yes soppy driver side floor board, but only in one big square, hood liner is ruined, i have watched rain pour in from the onstar, now a friend pulled off the little trim pieces where the carpet meets the body on both sides and water was puddled up in the tracks, it took 3 rolls of paper towels and was still soaking up water, and yes the electrical cords all running thru there, i am wore out with it, i wondered if a body shop could help, and ya say the seam down the whole top where it welds together has a sealant? oh my gosh, and i replaced the sticky seals on the top running lights, but ya say its the outer ones mostly?, this has wore me out and i have spent hundreds on some of the new door seals, but when i went to order the rest of them, its very confusing, i wish i had the parts numbers, the ones that attach to the actual doors, and the ones that attach to the body pinch weld, and the ones that go from front doors all the way back to above the back doors shaped like a 7 cant figure out which one those are either,

 

Reach over the black plastic roof tracks that the racks bolt to. Right behind them is an area that, for lack of better words is a “gutter” that goes front to rear on both sides of the H2. (I’m not sure if the H3 is similar but I would venture to guess it may be) At the bottom of this if you get a ladder and look down you will see where the sealant was brushed on and sealed with paint. This was where my problem leak was coming from.

 

on older earlier models that roof seam has a black trim rubber that covers it. so you can not directly see if the seam sealer that gm used has failed / cracked

 

As long as you come prepared in case it needs to be sealed you can just rip that rubber seal off. I’m sure it has some purpose but I ended up ripping mine off, then pulling as much of the old seam sealer out as I could and resealing it with seam sealer from Napa, comes in a caulk container and requires the gun. I will say, it’s important to note - you’re going to have exposed primer when you pull out the old seam sealer.

I didn’t monkey around and try to paint the area after sealing it but a lot of people aren’t going to be okay leaving that as is and may want to have to repainted.

I’ve owned my truck for 14 years and have put 3/4s of it 207k miles on it. I don’t ever plan to get rid of it. It’s in great shape mechanically but the body paint is starting to get rough, a little missing paint that cannot be seen without a ladder doesn’t bother me terribly. As long as there’s no rust that is.