Update:
I removed the headlight, some tips for those who want to remove theirs:
- When removing the bumper, a plastic pry bar/trim removal tool greatly helps when loosening the two tabs where the fender meets the bumper
- Unbolting the coolant tank and moving it aside, as well as complete removal of the vacuum canisters and bracket gives you a lot more room to work with.
So I opened everything up, dried it out in an air conditioned room. Don't place the headlight upside down while drying as you will get streaks from moisture condensing and falling towards the top of the headlight, ask me how I know
that was NOT easy to clean as access to inside the headlight is extremely limited.
From the looks of it, the rubber seal from the headlight back cover and seal from the cornering light access cover (one on top) were both in good shape, no damage and very elastic/rubbery. The hard seal from the headlight lens to the headlight didn't show any signs of wear/tear/leaks etc.
I took the headlight to an expert, he said there is no way water is getting through the hard seal. Said it was most likely the rubber seals from the covers. The guy actually was amazed the headlight was from a used car, I must be doing something right having almost 50k miles
What I ended up doing was flipping both seals and applying some grease. This gave both covers a much tighter fit and seal once I put them back on the headlight. I also removed the control unit (bottom of headlight) and made sure no moisture got in there, bone dry. There's a small rubber seal on that unit as well which creates a seal once you slide it into the headlight, so I applied some grease on there as well despite the seal also being in perfect shape. Closed that bad boy up and put it back on the car. I decided to do the same for the driver's side headlight covers, without removing the actual headlight from the car.
So far so good. I washed the car a couple times over the last few weeks and intentionally didn't avoid the headlight, zero moisture or condensation before/during/after the wash. The most likely culprit here, imo, was the cornering light cover seal since it sits on top of the headlight. I think water pools there and slowly works its way into the headlight.
Bonus pics! First time the car has ever been this exposed and I just had to take a couple snaps.
Here you can see the placing of the oil lines down to the oil cooler. They are closest to the corner of the back cover and may be wearing out the seal over time, though mine didn't have any visible wear compared to the rest of the seal.
Poor girl :'(
Here you can see the tabs on the bumper which meet the fender, knowing what they look like definitely makes them a lot easier to remove
If you want to attempt this without removing the bumper and headlight (which you really don't need to) then both covers are easily accessible from under the hood, although the back cover is a bit of a pain to get back in correctly. There are two tabs on the bottom of the cover which insert into two slots on the headlight, just take your time and be patient with it. Additionally if you also want to have a look at your control unit or suspect there is moisture/water in there, it can be accessed through the front fender liner which isn't that difficult to remove. Best of luck!!
TL,DR:
Problem: Moisture and condensation in headlight. Leads to adaptive headlight malfunction.
Solution: Remove headlight back cover and cornering light access cover (top of headlight). Flip seals. Dry out headlight. Put covers back ensuring a good seal. Problem solved
hope this saves someone from replacing their headlight/control unit, both of which are very pricey.