Question:
i know that the Nismo S-tune Suspension are the only ones that hold the factory warranty. But if i buy a set from a private dealer, is that warraty still valid or MUST i purchase it from a Nismo distributor??

 

Nismo S-tune components have a full factory warranty when installed by the dealer at the time you purchase the car. If you buy them and self/3rd party install, then all you get is the standard "parts" warranty. That is, if the part fails within a year, Nissan will replace it.

From the NISMO brochure (http://www.nissanusa.com/m/cma/v/nismo/350Z_webbro.pdf)

S-tune components are engineered for street-legal cars. S-tune components offer racetrack-inspired styling as well as credible increases in horsepower,
but with an additional feature that our aftermarket competitors can’t match – each S-tune component is covered by the Nissan Parts and Accessories
Limited Warranty – 12 months/12,500 miles or up to 36 months/36,000 miles if installed at the time of new vehicle sale (like any other Genuine Nissan
part or accessory). See your Nissan Dealer for warranty details.