I believe the key to importing "otherwise NAFTA" parts etc. is that they are 'labled', as to origin. If not, for sure there is a duty. That is one reason that Cdn. dealer prices are often significantly more that the exchange conversion on some (most) parts and not on a few (Cdn. made)parts. I have noticed this, particularily on some Ski-Doo parts. I believe also, that a 'friendly wrecker' can bring in some parts with less hastle, i.e. a NAFTA assembly, and remove the unmarked part.
