Usually, NOS in an unopened box is OK when it comes to fungus and such, but you never know for sure until you see it. An inspection period is the best bet, just to make sure everything is OK. If you can find out its age somehow that would be useful-seals are usually good for 15 or 20 years. I had an ETR-S older than that, which was fine without ever having had any work done to it.
Price is a factor: if it's cheap enough to be worth giving it a CLA (clean, lubricate, adjust) if it needs to have it then you really can't go wrong.
I purchased my Bronica ETRSi (which I again recently sold) new in the box. Everything worked exactly as it should - purchased body, back, 40mm lens, and hand-grip new. Perfect...never had a problem with any of it and I would certainly recommend this method if you can manage to find one. BTW I sold it off after using it for about a year and a half for more than I purchased it for...bought and sold on *Bay.
So, my experience was positive. Oh, and I only sold off the kit because I'm shifting my work methods and didn't need a 645.