I have a few thoughts on this, and some of your comments have gotten me thinking so here goes:
I was just researching this and talking to a Bosch engineer last week. Here is what I know.
1) The silicates (silcone) in antifreeze are death for an O2 sensor.
2) Silicone caulk or silicone lubes like spary on silicone are death for an O2 sensor
3) Silicone antisieze is death to one.
4) Any soap with silicates in it (which is very common) is death to an O2 sensor. Many cleaners like Fantastic, 409, most alkaline cleaners-detergents, cloths washing soaps, many alkaline steam cleaner soaps, some car soaps, have sodium metasilcate, most antifrezeze formulas have sodium metasilicate, and they all will kill an O2 sensor.
Aparently the silicone, or silicates can react permanently with the O2 reactive sensor materials thus deactivating them permanently.
That said, a good solvent based solution like seafoam, B-12, etc., keroseen, maybe deisel fuel, used as soak cleaner followed by a 500 F oven bake to remove carbon might work if the problem is carbon fouling and silicone contamination.
Also, a non silicated solvent based cleaning solution used in an
ultrasonic cleaner* might work great (*which we used for cleaning deisel fuel injectors that were previously going to be tossed as I recall, for the first time back in the 1970's
). I would still do the oven bake after cleaning with the ultrasonic cleaner. Might even do both steps twice just to get all the carbon out.
Of course, the question would be is it worth the time and trouble for one O2 sensor? But for these newer vehicles with 4, $100 sensors, it might be worth the trouble ($400).
Anyway, any nonsilicated, non silicone, pure solvent cleaner should be ok, including brake cleaner (the old chlorinated or the new non chlorinated ones.)
It also might be a good idea (cleaning) to improve the O2 sensor response time which degrades slowly with age! That would increase ones MPGs. Shame they are not easier to get to on our older jeeps. My sons ford 96 Taurus O2 sensor is a 5 minute job standing up.
Maybe some some younger, boared, bright young mind out there will read this thread, gather a few bad O2 sensors, clean them like I suggested above and them bench test them with a multimeter to make sure they are bad, then clean them as suggested above then use a propane bottle bench test set up with a multimeter and see if cleaning them brought them back to life?
And then of course tell the rest of us lazy know it alls how well (or not well) it worked.
If that were to happen, that person should test the O2 sensors first on the bench to verify that they were dead, before they were cleaned!
Anyone out there dying to run a few cleaning tests?
One last thought, if you get silicone or antifreese on one of these, try triple washing it with DI water several times followed by several good solvent washes and you might still salvage the sensor. Once the sensor gets heated up (over 600 F, in fact I think it is more like 1000 F at the sensor tip where the internal HEGO heater is) the silcone reacts with the sensor elelments and then it is permanently shot, then no washing will fix it.