Went ahead and replaced these last weekend (280,700 miles on ODO). The first time these were replace was Aug 2012 at 121,000 miles on ODO. So, 160,000+ miles doesn't seem unreasonable for lifespan on these.
So far, no downstream O2 codes, which I had constantly. Prior to this, dash lights would typically trip on after only a few miles of resetting pending & permanent DCTs (mostly P0420/0430, on longer trips I would get an occasional upstream code P0173/0174). Crossing fingers this week goes without any dash lights.
Once my skids were removed, it wasn't a terrible job to do, except a bit of debris in the face. Took me about 3 hours. My exhaust system bolts were not seized and everything came apart fairly easy. Having small hands and arms is probably my saving grace, since there are some tight spots to get a socket or wrench on. The manifold bolts came off fairly easy. I think the hardest was the forward driver side because the alternator is in the way.
I was really expecting my primary cats to look a lot worse and a bunch of crap fall out of them. The passenger side did have a small blockage.
Driver side
Once cracked with a 12mm deep socket and longer drive handle, I got in there with a ratchet-wrench. That upstream O2 sensor harness (upper left behind down pipe) gave me more headache than any of the bolts did. I ended up using a very small screwdriver to wedge the cantilevered lock open and then gave it a good tug.
New manifolds, gaskets and a few replacement studs just in case.
Didn't need the studs. I also reused my primary O2 sensors. I wanted to see if in fact these really needed to be replaced.
After the job completion and a few highway miles, they blued in real nicely
