The highest temperature RTV I’ve ever seen is rated to maximum temperatures of 650F, I don’t believe any silicone silastic can withstand the temperatures of combustion chambers, which can exceed 2000F.
I agree with those that say it’s a myth. I don’t see any way that fumes from curing silicone RTV can get through the combustion chamber and coat an oxygen sensor. If one were to suggest that it coated a component that precedes the combustion chamber I might accept the possibility, but not an oxygen sensor.
If there exists actual data from a credible source, I’d be interested in seeing it.