I've just experienced a similar situation to RW in a 2010 Volkswagen Passat CC with under 30,000 miles. The pulsing vibration on braking was very bad indeed and had gradually worsened over time. The inner face of one rear disc had two severely localised corrosion areas, which effectively reduced the thickness of the disc at that point and caused a pulsating action on braking. This, as you often point out, is due to prolonged static periods with the parking brake on. This causes increased electrolytic corrosion between the brake discs and the metallic content of the brake pads by trapping moisture.