I wouldn't opt for buying a replacement from Nissan as it'll more than likely costs you over £250 for the pair. I would buy aftermarket, kyb are an excellent item. Rear suspension is a divorced setup, no need to touch the springs.
https://m.autodoc.co.uk/kyb/829789
https://www.torqen.uk/nissan/350z/suspension-steering/springs-shocks/810-350z-kyb-excel-g-rear-shock-344455.html
Aged dampers can fail at any time.
Items aren't sided