Thanks for the warning.
If your mechanic "cleaned" the O2 sensor or its housing, that may be all it needed. Most just need to be cleaned, along with the connector.
Too many people spend too much money, just because they believe what they see on the scanner. DTCs are a good place to start the diagnosing process, not the end of trouble shooting. Eg: if you get multiple misfires, one of the codes says the cat converter is bad, not true but that code will not go away after the misfires are cured. The car's computers are not logical, it is up to the owner to use a bit of common sense.
That is what the Brickboard is all about. Getting second opinions never hurt.

Klaus
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I still miss my 164