Code P0014 is for the exhaust valve timing control bank 1( the passenger side). Unless you also have code P0024 which is bank 2(driver side) there shouldn't be any reason to have to change both sides. I have changed several valve timing covers on the G35's and I've only changed the sides that were throwing a code and no car has ever come back again with the engine light back on. I would have only the right side replaced. Do you have a lot of miles on your car? The VTC cover is a powertrain warranty which is 6 years/ 70,000 miles.