Been having problems with a leak that ends up with water getting in the rear, lower wheel well area. Doing a water hose test I found all 4 tail lights lens leaking around the O.D. Taking one side apart (2 total assy.) the top tail lamp assy. and the lower back-up light assy. I found the following: the front half of the assy. (lens part) did not fit tight with the back, rear assy. Bracket! The fit was uneven and the gasket was flat in areas so it didn’t make contact. See parts drawing at … HTTP://WWW.GMPARTSCENTER.NET/AUTO-PA...AIL-LAMPS-SCAT
There is a gasket between the front and back halves but no replacement part per the GM Parts Division that is listed, as you can see in the drawing. I can get/replace the back halves / brackets but the gasket will still be low in areas.
Then I was thinking of making a gasket out of thin rubber to fit between the outside of the body and where the outside lens mounts. This will / should seal the lens… or get some NON-HARDING sealer to use in this area… or where the front and rear halves meet. AGAIN…. like many have stated about many things that GM has made, this was a poor designed area.
Anyone had this problem, anyone got a fix and I just hope this is all that is wrong. YES and by the way I checked the drain lines, clamped and seal them in the tire well area where they go outside the well to empty. Tested this again and was good… never tested BAD. Thanks for all help, JC

 

If you're sure that's where it's leaking in, then just seal it up.
Some 3M RTV sealer, black or clear, should do the job.

I did the "Find the Leak" thing on my Dodge truck a while back. I swore it was the rear sliding window, so I did a seal up on it.
Wasn't the window leaking.
Wound up being the cab mounted 3rd brake light. The gasket had shrunk up over the years apparently. I pulled the light assembly, cleaned the gasket and it's contact areas. Put a continuous bead of black RTV on both sides of the gasket and reinstalled.
Hasn't leaked since.

 

The gaskets all shrink over time, RTV or butyl sealant will seal it up. But even that will leak eventually, and GM didn't make the gasket they just sourced it!

 

Now don't mistake this for saying you did anything wrong or goofy, but I've seen enough odd things here over the years to draw the conclusion that nothing is impossible.

From your description JCC, and I might be misreading it.

It sounds like your gaskets ended up inside of the quarter panel between the taillamp bracket and the inner quarter panel. Instead of being in their proper location between the taillamp and the outside of the quarter panel as illustrated by the replacement lamp assembly below.



If the gaskets are in the wrong location, your HHR will leak like a seive around the lights.

 

Thanks for the input and support… here is what I did, Oldblue said to try the Butyl rubber sealant products. This is new to me and I wanted to try it, finding it was harder and took more time than doing the job. To help others with this part here is what I found… At Home Depot they have Elastomeric Butyl Rubber Sealant TAPE made by GSSI Sealants, #99415 Tape Butyl, 3/32 X ˝ X 45’. I put a strip around the lens on top of the old gasket, simple fix (see Reply #4 which shows the outside lens, back view, tape was put around the dark area… THANKS to 843de for the photo). There was still a gap in places around the O.D. of the lens (see Reply #4 the O.D. red area of the lens), so I filled this with RTV (clear). After 24 hours (plus) of rain/ storm I check the inside of the lens compartments and the wheel well… all dry, no signs of any water. Will keep checking it but it would have lots of water as before cases in the pass.

Here is a noted problem I found… on ONE of the lens which was leaking the most I found a push on small rubber clip in the hole where the lens mounted. I found no others? This kept the lens from fitting flat against the body, also noted that the inside back half of the lens had been kept from fitting flat also and had broken it and pushed it up in this area. I am sure this is the area that was letting in most of the water but like Firemangeorge stated it’s not a sure thing. Yes I too was thinking it was the drain lines from the roof but not so. I removed the clip and all fit tight. So far it is good but will keep checking….

At Ace Hardware I also found Butyl Rubber #10204 in a large caulk tube size, WH- 10.1 oz., for those needing / wanting a paste tube product of Butyl rubber.

 

Glad you got the water leak fixed!!!