Mercedes coating I consider a noise reduction coating. More than a rustproofing one anyways. I cannot remember but it is probably not inside the rocker panels.

Drilling the typical 1/2 inch holes for the plastic caps and spraying in oil and grease mixed. It will creep everywhere in there and give decent protection. Attempts to rustproof Mercedes cars of that vintage overall are almost impossible. Driving them here all year long is suicidal for these cars.

Volkswagon used a great system from the factory. Production levels did not allow the Mexican workers to use it properly. It was elecroplating a thick layer of sacrificial metals on the shell. It was hit and miss if you got one done properly as intended by Volkswagen.

It added substantial weight to the car as well. That is why they had the twelve year rust penetration warranty. Yet it pretty much took a court case to get them to honor it. As they are all too aware that the quality control was lacking.

On the Jetta the wife totally wrote off there were two areas of separation from the parent steel. At least 1/16 inch thick. Of sacrificial metal. Those shells had to stay in the electroplating tanks for some time to get a coating that thick built up. I believe that program no longer exists as it prevents rapid production. I know their 12 year warranty is gone for a long time now. Against rust perforation. Wolfsburg designated Volkswagens where made in Germany. My feeling that quality control there was kept up.

To be fair to Mercedes their market was primarily people that do not keep the car too long. They would have been all too well aware of what their coating could result in. Being in the proverbial rust belt or in certain climates.

Volkswagen does not do well against owners that use small claims court. Volkswagen customer service reps where given a list of 10 or 12 denial of rust claim items.