« Reply #1 on: 23 February 2013, 11:26 »
You don't park near a railway line do you?
About a thousand years ago I used to have to park near a railway station and my (at the time) white mk1 GTI used to get covered in this brown rash that looked a lot like that.
It turned out to be brake dust from trains (like tiny bits of iron) that pitted the paint.

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‘25 8.5R, ‘23 8R, ‘20 8CS, ‘19 135iX, ‘19 TCR, ‘17 Ed40, ‘17 GTD, ‘15 7R, ‘13 GTI PP, ‘11 GTI, ‘09 GTI, ‘98 Ibiza Cupra, ‘05 GTI, ‘06 Polo GTI, ‘04 GT TDI, ‘05 Fabia vRS, ‘02 GTI T, ‘03 Ibiza TDI 130, ‘01 Leon 180, ‘89 mk2 16v, ‘99 Ibiza TDI, ‘96 VR6, ‘98 Ibiza TDI, ‘92 VR6, ‘88 mk2 8v, ‘92 Polo G40, ‘91 mk2 8v, ‘89 mk2 8v, 205 GTI 1.9, ‘83 mk1 GTI, ‘80 Scirocco GTI, plus some others I’ve forgotten