Hi Mambo,
Hopefully you will take heart from this slight hiccup and note that the dealer is actually replacing the rusty part and NOT carrying out a shoddy bodge job. I will keep repeating myself.
I would NOT be happy with a chewing gum type filler repair. Fitting new parts where possible is a must. Clearly there will be locations where this might be difficult or indeed impossible to actually acheive.
The friendly, polite approach will pay dividends every time. To get all official and demanding will only put peoples backs up. I am sure you will be the former and good luck with the visit.
John