Assuming that both discs and the pad set have been installed for the same length of time, possibly some contamination has happed by way of some form of grit, therefore scoring the disc.
Brave man, I'm very impressed that you went through with it.
We popped into Apex last year, as we do during most visits to Nurburg. Misha and the crew are always good to chat to and very welcoming.
I've been using Auto Finesse Aqua Coat for the last couple of years. I tend to spray it on to the rinsed and still wet panels every fourth wash. I'm sure there's better, but seems to give good results.
I might try the AG one for a change next time.