....I now a few dealers back then changed tanks and drums ,even painted under carriages.This was on GN's that were getting sold over sticker .Without question they did (clean up the 2 X's they had allocated to them.The 2 they bought from low volume rural (small)
dealers needed nothing done.
Also think though that's just a handfull out of 547.....I'm sure a few may have slipped through the cracks which is why you see so many rusty ones today. Just my observation.
As an aside, I've bought a few expensive "collectible" cars new and never really paid much attention to the undercarriage. Why would you it's supposed to be brand new right?? I didn't really even think about it and kinda took it for granted. Fortunately they use more aluminum and stainless now vs then so it's less of a problem and they still look pretty good.
I also didn't become that interested in undercarriage condition until I noticed more and more focus on them in the collector car community. I have seen numerous posts with people pitching fits about how rusty different GNXs are underneath. I myself am guilty of such until I started looking more and more. Anyone ever really stop to think that maybe they came that way?? I think the pictures show they may have.
Anyways, after seeing such I began to look closer when I would go look at new cars on a dealer lot and believe it or not the unprotected metal parts are already rusty even here in warm mostly dry TX.
Just my observation whatever it's worth.