There is a sticker on the top of the radiator tank with the Calsonic name and a part number. The most common part number is 21400-EA215, although some have reported the number 21400-EA265 (which doesn't show up in the Nissan catalog). This is the original part number. At some point under the -EA215 number, Calsonic apparantly correctly the design of the cooler that lead to problem of coolant contamination. Later, the part number was superceded to "21400-9CA2E." It is unsure of exactly when Calsonic corrected the problem, so any of the -EA215 or -EA265 radiators installed on 2005-2010 Pathfinders/Xterras/Frontiers could develope the crack and result in cross-contamination, but so far the majority of those occurances are limited to 2005-2007 models and a few 2008's, so far. Time will tell if the problem will be seen on a greater number of 2008 models and/or progress into the 2009-and-later models. Keep in mind that not all of the -EA215 radiators will fail and experience cross-contamination issues; in fact, it is only a small percentage of those radiators that will fail. The big problem is the extent of damage and cost when those radiators do fail. Nobody wants to be on the hook for a $5000-$6000 repair bill, especially if it can be prevented! The one thing we do know is that the 21400-9CA2E radiators are of the updated design.
Radiators with integral transmission coolers have been used for decades and some even use an integral cooler for engine oil, as well. With the exception of the current problem affecting the 2005-2010 Pathfinders/Xterras/Frontiers, these coolers have been very reliable and trouble-free. I started as a Nissan tech back in 1985 and can't recall ever seeing a failed radiator cooler line (as far as cross-contamination issues) on a Nissan vehicle up until 2005. The issue at hand is either a failure of design or manufacturing by Calsonic, which ironically has made the radiator for the 2004-2005 Titans and Armadas which have a problem of the bottom tank cracking and leaking. Myself, I would feel very comfortable in using an aftermarket or updated Nissan radiator to replace the original -EA215 radiators.