The new radiators were supposedly updated under the old part number 21460-EA215, but there's no way (as far as I know) to tell the differance between the old and updated style radiators. Nissan later superceded the part number to 21460-9CA2E; those we know for sure are the updated design. So far, almost all of the radiator failures have been on the 05-07 models, which did not have a V8 option. I have only heard of a couple of '08 models that have experienced a radiator failure and they were V6 models (which would make sense since the V6 is much more common than the V8). It's hard to tell right now if the '08's are going to have the same rate of failure as the first gen R51's or if they'll be limited to just a few. Nissan's extended warranty on the radiators includes models up to 2010, so for now, I guess it's a "wait and see" situation.
As far as replacing it, it's kind of a pain in the tail! I did the one on my 06 Pathy V6 when I did my timing chain job and spark plugs. Unlike earlier Pathy's where you could just drain the coolant, disconnect the hoses, remove the lower shroud section and a couple of bolts and pull the radiator right out, the R51 is designed differently. The R51 rads have side brackets bolted to them with the mounting posts. The AC condensor mounts into the radiator brackets, so the radiator has to be tilted forward and the condensor lifted out and supported with rope or some wire to keep in from dropping down. The next obstacle is maneuvering the radiator out and between the AC lines going to the condensor. I replaced mine with a new, $92 radiator I found on Ebay with a lifetime warranty. Yeah, it was made in China (what isn't these days), but it appears to be well built and the fit was perfect. There are two different types available: a single 2-1/4" core and a dual 2-1/8" core. Both are the same as far as mounting. Which is better?...Who knows? The original was the single core; I chose the dual core to replace it. I also replaced the four foam seals on the radiator and brackets; they aren't expensive from Nissan and they make the job look more professional. I also replaced the thermostat with a genuine Nissan part while I was in there. The labor guide shows 3.1 hours to R&R the radiator and that's about right if you have a shop and the tools to do it. Might take one a bit longer if they are going it on the ground with hand tools. Just glad it's done and over with!