General Maintenance & Repairs - Still having problems...

Well I did a tune-up, my gas mileage was ok for a while, but now it's back to crap. My exhaust spells strongly of gas and I know that I need new O2 sensors...but when I called for prices, the parts person made it quite clear that the O2 sensors don't go bad on their own, that they are fouled by something. He recommened replacing the EGR Valve or emmissions temp sensor. I'd really appreciate some more opinions.

O2 do go bad but usually it is something else that causes it... Are you running Cats? bad cat could cause it to be bad.

First time I seafoamed my car with 90K+ miles on it, it fouled out the O2s

yeah i still have the cat, and I haven't noticed the smell that came with my last cat that went bad, just gas