When I bought my expedition 12 months ago, both the rear trailing arms and the rear upper control arms (amongst quite a few other things) had to be replaced. I had the dealer do it (negotiating the repair costs in with the purchase price) prior to me driving it off the lot. The trailing arms in particular were absolutely horrid, both would've snapped within no time. They were so bad, in fact, that it wasn't safe to even test drive.
Now, I'm originally from upstate NY and know far too well the accelerated deterioration inflicted on vehicles by the snow, salt and extended winters. When reviewing the Carfax report on the Expedition, one of the things I was specifically looking for was where it had been located. With two previous owners, the truck had never been garaged farther north than Virginia. Obviously we still get snow and ice here, but nowhere near as much, as often or for as long as the northern snow belt states. Taking into consideration my Expedition's age (2000), Mileage (109k miles when purchased), and known garaged locations, the deterioration of those trailing arms was still surprising to me. Being that bad, they probably should have been replaced at least 20k miles earlier if not more.
I'm glad this thread stayed active because up until now, I had assumed that since they had been replaced last year, I probably wouldn't ever need to replace them for as long as I have it. Unfortunately, because they were replaced at a dealership using (what I would assume to be) the same poorly finished OEM parts, now I know I'll have to keep an eye on them in the future.
In case anyone was curious, in addition to the parts, the invoice reflects a 4 hour labor charge for the trailing arm replacements and another 5 hours for the rear upper control arms and the brake hose assemblies’ replacement combined.