Now the "can of worms" bit.
The first thing I noticed after looking closer at the headlamp, was that the plastic sidelight lens was burnt, melted & ugly. The second was spotting what I'm sure was the cause of the dampness getting into the headlight. I wonder if this is why so many here also report having the fogging issue?
With the access cover off, I noticed at the outer end where the cover hooks in, instead of clamping down on top of the seal, the edge of the cover had instead pushed the seal aside making very poor contact. Looking at this further, It's obvious this is a case of poor design, and I later found the other headlamp had the same issue, though that one seems to have stayed dry inside so far.
The idea of course is, you slide the plastic "fingers" of the cover into the receiving holes on the housing, with the cover tilted away from the headlamp, then press it down and pull over the wire clip to secure in place.
I didn't manage to get pictures to demonstrate, but the problem is, that as you tilt the cover into position, the face of the seal stands so high that the lip of the cover can't clear it as it "rotates" down into place. This is worse still if refitting the cover with the unit still installed in the car, as, due to the plastic mounting frame being in the way, you cant get much of an angle at all as you slide the cover into the holes.
My solution to this was to flip the seal over in the recess with the worn face down, so the rest of the cover would seal more securely. Then I carefully with a fresh sharp blade trimmed the problem section of the seal down flush with the top of the recess it sits in. This is not Ideal, as it exposes the possibly porous inner foam core of the seal, but it does then allow for the edge of the cover to sit down centrally on the seal as it should do, and there's still ample compression, even having trimmed off about 2mm from the height.
Another probably better idea would be to smoothly trim a little off the plastic lip of the cover at that end to achieve the same result. On reflection, I wish I'd done it that way as it would've been just as easy, and wouldn't have compromised the smooth finished surface of the seal!
Here's a Paint sketch I just knocked up to try and clarify:
Now for the melted sidelight issue. The same had also happened to the left sidelight, only on that side it had caused the bulb to become well and truly stuck in place, that it had to be forced out after first removing the plastic lens assembly from the headlamp.
I find it very strange that this problem exists at all, as this seems a very poor design choice. It's all the more strange that this only seems to happen to some A2's (I've only found a couple of posts from others mentioning this issue here).
Both sidelight bulbs had clearly been in place for a long time given how blackened the inside of the bulbs were (as you can see in the photo below). They were also both the correct wattage (EDIT: or not, as
@Proghound has pointed out, they should be 3w, and the P/O had fitted 5w!). I'm sure the damage occurred or at least got worse with these bulbs fitted, given how jammed in place they were.
I wonder if this is a problem of some batches of plastic used for the lenses not being heat resistant enough, or whether it's certain dodgy bulbs being hotter than they should be for the given wattage? Anyone have thoughts on this?
After about an hour of carefully chipping, scraping and filing away the lumpy & brittle burnt areas of plastic, not only to improve the appearance, but to restore the internal diameter to give space for the new bulbs:
The photo below is after doing the work on the left sidelight lens a few days later & shows the amount of material I had to remove from just this one lens, along with the various tools needed and the replacement bulb.
I'm not a fan of retrofitting LED bulbs without very good reason. In this case though, LED's are definitely the way to go, as they run much cooler and will avoid any further damage. It is, though very necessary to clear all the blistered plastic out of the lens, as the LED wedge bulbs are slightly wider, and won't fit otherwise.
Not perfect, but a vast improvement, and all back together:
