Headlights problems of the 2009 Volkswagen Routan

The electronic door (side panel, passenger, and driver) door locks stopped working. At about the same time our front headlights began to intermittently go out during operation of the vehicle, and then stopped working altogether. The vehicle was submitted to the dealership and customer was informed that the headlight ballast was worn out and had to be replaced. Parts were ordered and when the vehicle was taken in for said ballast replacement another mechanic stated this was not a ballast issue since the headlights appeard to turn on during ingintion, but then stopped working shortly afterwards. We had to wait until the next day for a dealer electrician to look at the vehicle. The electrician determined a corroded control panel was causing a short and likely causing door the headlight, as well as other issues such as incorrect tire pressure and speed indications and possible fire. No water was introduced to the vehicle, so my question is how does a control panel corrode unless there is a faulty voltage issue and electrical design defect? the mechanic indicated the dealer gets a lot of these issues on the Routan but there is no recall so they charge $900 for the replacement panel. Vw knows of this issue that their own mechanics indicate can start electrical fires! the company should be investigated.