First off, Welcome to NICO. OEM exterior parts?
http://nissanparts.org/ Select the products button and then the Nissan Parts Catalog. I have ordered parts from them and never had problems. Also, they are a sponsor to this site.
http://www.everythingnissan.com/ is also a sponsor. I would try either of them first.
As far as your transmission, I would first make sure that your transmission fluid isnt low and then trace the problem from there. bud