Alright so I think this was the issue.
As I predicted before, the ballast is on the side of the headlight on the STS which is why it never had any failures even with all the water in the headlight. But clearly the last person inside this ballast cover completely mangled the gasket upon installation and I think this was admitting water into the housing. At least, this is the only thing wrong that I could find.
Of course it is discontinued. The passenger side is not. Come on. Plan B. Black RTV. Moving along.
Then I had to finish melting all the ice. It did not melt overnight in my garage. Well some did.
Then I rinsed the whole inside housing with distilled water. I just wanted to remove any contaminants and hopefully some water staining. Then let it all dry. That's looking better now.
The patient waits. Plenty of room to work on normal size cars in my garage. There was room to walk behind the car and still this much in front of it. And this isn't a compact car.
Just a shot of this for posterity. I thought it was funny to see the tire through the headlight cut out due to pulling the front wheel house.
This is the harness that goes to the headlight assembly, then there is wiring internally to do whatever. Anyway this didn't look that great so I soaked it in contact cleaner, compressed air dried it, and goobered some dielectric grease on the pins.
Look! This is my black RTV solution. I put a bead under the gasket, and then on top of it. That should work. And leave a mess to clean up if I have to replace the ballast some day. If this actually keeps water out, maybe that will be years.
The other end at the housing. The ballast looks totally different than the SRX FWIW.
All covered up. Just one screw.
A close look at some of the smooshed RTV. I'll leave the car in the garage overnight which maybe will give it a slightly better chance to cure properly. By the way, I am really liking this old digital camera. It focuses so well, the strobe flash is great and it's just nice not to have to bother getting grease all over my phone. The small inconvenience of transferring the pictures to my computer is WELL worth it (the phone auto uploads to Onedrive).
Ah now that is so much better! This better have fixed it.
Look, no pool!
Another shot.
Even better - it looks just like the passenger side now.
Here is one of the inner wheel houses I pulled out (didn't have to do this on the SRX...). Take a look at that date. Clearly this car had some kind of front end accident.
Before I reattached the bumper fascia, I decided to clean the fascia and the fender where they meet to prevent abrasion stuff.
Here it is all reinstalled. So nice for this to be dry. I will be quite pleased if it stays this way.
Oh, here's some bonus stuff. This fell out of the lower wheel house area. Looks like a windshield washer cap or something.
Also check this out. I've had this CFL shop light for at least 10 years. Probably more. It was just a $20 one from Walmart. Never replaced the bulb. Finally the cord has failed (ask me how I found out). I MIGHT try to tape it up. Not sure yet. Light still works. How about that?