The Nissan Path

2010 here approaching 60k. Just curious, is there a way to know if I have the defective tranny? I know there's a thread on here I'm sure pardon my laziness

It's not the transmissions that are defective...they are actually very good. The problem is the radiator. In the lower tank of the radiator is a cooler tube for the radiator that both cools the ATF as well as heats it up to operating temperature quicker. This design has been used by auto manufacturers for decades fairly reliably. The problem in the 2005-2010 Pathfinders, Xterras and Frontiers is that some of these cooler tubes have cracked and allowed cross-contamination of the engine coolant and ATF. It's the coolant in the ATF that has caused the transmissions to fail. Most of these failures have occurred in 2005-2007 models. So far, we have only 1 reported failure on a 2010 Pathfinder, so chances are pretty good (so far) that you won't have an issue, but those chances are obviously not 100%. If you are within the extended warranty for the radiator, you don't have much to worry about. However, once you get past the 8 years/80000 mile "free" period of the warranty, you may want to consider the "bypass method" or radiator replacement as a preventative measure if you have concerns.

Can I take it to a Nissan dealer and have them replace it anyways? Or does it have to fail in order to replace?

Warranty doesn't cover parts that haven't failed. The only hope of having them replacing it before it fails if they voluntarily recall it under a campaign, which seems unlikely at this point, or if the NHTSA, which is investigating the issue, deems it a safety issue and forces Nissan to recall them. The only good news is that while the "updated" Nissan radiator is pretty expensive at $550, aftermarket radiators are relatively inexpensive, currently selling for as little as $73. Unfortunately, unlike earlier Pathfinder models, the actual job of replacing the radiator is a bit of a pain. Book labor time is about 3 hours, whereas on older Pathfinders and Nissan trucks you could replace a radiator in an hour or less.