it's not possible to buy a used catalytic converter from a junk yard, legally. U.S. Federal Law prohibits the sale of used converters.

However, it is possible to sell them for scrap. I have helped multiple friends with emission issues, and used OEM converters can be sold for anywhere from $30 to $300. Large SUV types bring top dollar. In Dallas, some SUVs have had theirs stolen, b/c they are so valuable! Apparently, thieves are using battery powered cut off tools to remove them during the night, while they are parked.

I understand the after market used cats have minimal salvage value.

I was getting 2-3 years or about 30,000 miles from aftermarket Bosal catalytic converters.

Since my 1990 240DL is now 24+ years old, Texas only requires a safety inspection, no emissions test (two stage, on a tread mill test).

The other bonus is that the inspection fee is only $14 instead of $39.75!
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If it needs to be maintained, repaired or replaced on a 1990 240, I've probably done it. '90 240DL, 359,730 miles, will she make it to 400K ?? >>You haven't really worked on a car until you draw blood<< :-}