Here's a thread from WAY BACK that answers a few Z questions...
Sick of SUV's thinking of a Z
2003 & 2004 are the years that tend to have problems with the window motors and can also develop a grind/notchiness when shifting in & out of 3rd gear
(here's a post about the 350Z transmissions). The Track & 35th Anniversary (6MT) models from 2005 and all 6MT models from 2006 have had potential oil consumption issues. I've got a 35th Anniversary and never had any problems, so not all of them have it, it was a large enough problem that Nissan issued a TSB with an oil consumption test procedure and many owners had their engine replaced under warranty.
Nissan went with a new engine design starting in 2007 that has dual air intakes and produces more power than the earlier engines in 2003-2006. If you can I'd try for one for the newer HR engines (2007-2008) if you have the budget and never don't plan on modifying the internals of the car too extensively. I'll let our resident big power guy (JerryD) talk about that though. The '07-'08 models also have a more refined interior than the older models - but that's probably not why you're buying one, is it?
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