Audi A1/S1 headlight water ingress

[Syxi]

I bought my 2016 S1 early this year, and very soon after noticed dried drip marks on the right headlight, on the inner surface. After a car wash, fresh droplets would run down on the inside, and even a new drip mark appeared on the "floor" of the headlight. There was what appeared to be a very long crack on a seam on top of the headlight unit, which was the presumed culprit:

The entire headlight housing was replaced. Back then, I also checked the left headlight, and it had no such drip marks, but I don't recall (and looks like I didn't take a photo either) what the seam on top looked like. Well, just now I noticed dried drip marks on the left headlight, and the seam looks cracked, though not as badly as it was on the right headlight:

I've been told that water leaks in headlight units is a fairly common Audi problem. I've also had to have the left rear light unit replaced because it was literally coming apart at a top seam, letting in such amounts of water that the rear light would occasionally flicker and it even caused an error message on the instrument cluster display! We've had various cars in the family, some with far higher mileage, and we have never seen issues like these!

So now I ask; is this a known issue with these Audi headlights (sourced from Hella)? Searching revealed only condensation issues.

 

[Syxi]

One guy told me that what I thought was a cracking seam in the plastic is just the edge of a protective film applied to the headlight. Upon closer inspection this does appear plausible, which would mean the leak is somewhere else. Doesn't really change anything...

 

[Syxi]

Heavy rain today while I was driving, photo taken 3 hours later. Yes, it's all on the inside.

How on earth can a 2016 car with less than 24k miles driven have issues like these? Soon only one rear light will be original. I've never seen such crap quality before, not even on Fiats. Fortunately, being based on an entry-level car, the headlights are at least relatively cheap.