Brand new chassis do sit on the shelf, or box for a long time, before sold, back in the late 90’s to mid 2000’s chassis were very durable
Now adays are manufactured to be a lot softer, and will perform very well, as they flex everywhere, I just don’t know how many years you can get out of new ones now, but my gess would be 5 to 6 years? (if you wanna stay on top with the major racers)
But for the club level racing shouldn’t be a problem at all.
If these chassis you’re talking about at your buddy’s garage are only 1 weekend old, I would say they are still pretty much new, except for the brake system.
What brand of manufacture are they? Tony Kart, CRG, Top Kart, Etc.
I would say if the deal is good JUMP ON IT! Taking in consideration you’ll need to re do all your seals, at least. But as far as fatigue on the frame goes no worries there. What year are they?