Lead Poisoning

Can someone tell me how to know when an Oxygen sensor is going bad due to lead contamination from leaded fuel?

I have an F.A.S.T. O2 sensor and it sticks on one number under any circumstances... It should be changing, but it won't.

I bought another sensor for it, but would like to know what to look for when this one goes bad.

Unleaded race fuel is $$$$$$$$$$$$$$$$$$$$$$disgust