Unfortunately Rusting on the brake discs is a Porsche thing, apparently :sad:
When I changed the disks and pads on my Boxster, I opted for Borg and beck discs to attempt to lessen this, the Borg and Beck discs are completely coated in " BecTec " anti corrosive paint, even through the vents, this is removed from the friction surfaces once you apply the brakes when driving. Obviously this does not stop the friction surfaces from surface rusting after washing the car or being parked up in wet or damp conditions.
Almost a year in and the discs still look brand new, no rust whatsoever :thumb:
One thing that 99.99999% of drivers don`t do is clear out the cross drilling holes through the friction surfaces, which get full of dirt, gunk, brake dust and obviously hold water when parked up . Blowing them out, or poking through with a drill bit with the wheels off every few months will certainly help :grin: