yea its not the just the paint cracking, its cracked all the way through. its really not a big deal you cant even notice it unless you are way up close.. can barely notice it in the pics.
when i bought it there was a tiny "z" marked in window paint on the right lower corner or the rear windshield, maybe it was replaced at one point in time and thats what the crack above the b pillar could be from.

ill just buy a whole new plastic piece whenever i find a site that sells them. would go to the salvage yard but its rare to see any 370z's around here..

it's on this page:

767 Body Side Fitting :: Body(Side & Rear) :: Genuine Nissan Parts :: 370Z Parts (Z34) 2009-2012 :: Nissan Parts, NISMO and Nissan Accessories - Courtesyparts.com