2008 4runner 4.0 V6 with 290K miles. Started throwing P420 and 430 codes. Already ruled out all other causes (leaks, head gaskets, oil, O2 sensors, A/F sensors, etc.), and the live scan data one every machine I use says it's just out of O2 storage capacity when challenged due to the wave forms of the O2's. Ebay Federal EPA cats are around $220 for the pair from a dozen or more sellers. Rock auto's economy brand is about $350 for the pair. Factory or walkers are 900 - 1000+ per side. And then there is a weld on Magna-flo that is $211 per side + the labor to have it welded on.

Who here has actually used a NON-FACTORY replacement cat from the ebay sellers and had it work? If you did, where did you buy it?

Need some real advice before I spend any cash on this.

I've never bought an ebay cat, but the ones in my signature are super nice. Way overkill for our trucks, but will last a really long time.

Do you mean the ones welded to the manifold? If so I got my passenger side one from Rockauto as I wanted a real warranty, so far so good after a couple years. When I looked it appeared that the E-bay ones all seemed to be from Canada. With what you can get recycling an OEM cat you may be able to cover most of your cost.