oh right
yeah you'll have to take the manifold off, it's not a small job though. set yourself a weekend aside
while you have the whole manifold off, replace all the clamps and coolant hoses that run under the manifold and behind the engine there is something like 7 or 8 of them
they will cost you about $300 from nissan but it's well worth it while you have the manifold off because it's a f**king cunt of a job to do with the manifold on, practically impossible really (i had a hose under there split on me a while ago)