I am ordering new motorcraft o2 sensors anyways, but my local Mechanic (here in Mexico) said it's a very common practice to dip the tip into some muriatic acid (which is commonly sold in hardware stores here to unclog drains). This supposedly cleans them and restores their functionality. I'm really not inclined to try this myself, but if you're in a bind; who knows it may be worth a shot. Anyone else ever hear of this? or confirm that it works?