[wayner]

I believe there is also an exemption for vintage car parts versus nwesew ones.

Newer ones definitely fall under nafta duty and import rules

Exception are anything built in the US, canada or mexico
with some exemptions for vintage parts I believe???

If you have never paid duty on foreign parts, you should thank your border agent for deciding that it is not worth the time and paperwork to collect the duty. On a busy day you might just get waved through with no duty or taxes whatsoever.

groceries and children clothes are also exempt.