My car's on 160,000 'import' km so far and doing fine .
Reason being, as stated previously, actual mileage of engine is probably far more combined with cramming loads more air (than standard) @ high rpms.
http://www.amayama.com/search?q=63842-24U00
http://www.amayama.com/search?q=63843-24U00
Not sure if they're the correct ones, but ask your local Nissan dealer for those part numbers.