In the following picture, the parts painted with rust protection primer were completely gone due to rust and are replaced now:
The edges of the part that holds the number plate needed replacements, too (again, see areas painted with rust protection primer):
There is no way to replace the support structure with the outer sheet metal parts in place, so they need to go:
It is obvious that parts need to be replaced...
(some numbers are wrong in this sketch!)
After the 3rd iteration...