This is not only rust, its corrosion. Its from the inside out. They rot. Rust don't rot MB, corrosion does.
On my previous E the front , the middle ish, the back and the perch had to be welded due to corrosion. Brilliant!
As I said previously, there are metal fences here is Scotland that have been exposed to the weather for 200 years, and guess what, they are still standing strong. MB after 4 / 5 years start to already rot. After 10 years its structural damages. This is unforgivable for a company.