I'm With the above guys re the mud n muck behind the arch liners. We Perhaps tend to be lulled into a false sense of security when we see the all-coverring plastic inner arches, and assume that behind them, the car is as new? On older cars, i would have been hosing all this sh1te away on a weekly basis. Rather more time consuming to drop liners.
Owt for Nowt?
For what it's worth, I would also add...
I've just taken delivery of a brand new VW Tiguan.
There are foam inserts in the top of the inner wings, as seen from inside the engine bay.
Never mind the ones I can't see!
The VW evolution, or "improvement" appears to consist of encapsulating the sound absorbent foam in a plastic bag!
Manufacturers don't give a sh1t, as long they have your money, and their liability is discharged.
In the Mk5 example the problem, from their perspective, seems to be the combination of corner cutting design/spec with an over generous corrosion warantee!
Clearly they think that putting the foam in a plastic bag will see out the duration of their liability by warantee?
I would be willing to bet that mk7 Golfs are similar?
Seen this sort of scenario, for years, over all sorts of industrial plant and a wide range of OEMs.
As the man above said, we need to get away from the idea that they want YOUR asset to last