D402

300mm is correct, I bought these https://www.eurocarparts.com/p/brembo-brake-disc-10444224A which haven't rusted despite only occassional use through the winter. The outer side of one of the original discs rusted badly and wore the corresponding pad out prematurely, so I'd agree that the OE discs are rubbish.

I have a similar sloping driveway to reverse up and my DSG does the same as yours, let's hope it's normal

First MOT passed

Oh yes, drove me mad too in my first Superb. I eventually discovered that it was the rearmost section of the cover (the bit with the handhold) flapping about - fixed by carefully bending the crossbar piece into a very slight arch shape.