is there a way to find out if the oxygen sensor is bad, without taking it in to a mechanic?

i've got a 1992 300CE with 166,000+ miles...
i'm not sure if the sensor has ever been changed (i'm third owner), but i am experiencing strange throttle response changes....in the morning after a good warm up, the car is peppy...but afternoon evening or after the car's been driven, the car is sluggish off the line...even hesitates sometimes...

i've notice a drop of 1-2 mpg also and all this happened so suddenly and quickly...within a 2 week period of time...

i read somewhere on ebay (a vendor selling non-spec o2 sensors by bosch (where you have to splice them in)) that gave all the similar symptoms i'm experiencing, and also pegged my mileage in the range when these things go dead... i.e., 10-12 years or 150-170k mileage....

is this true?
anyone?
please help.....

__________________
~there is no spoon~

1984 300CD Turbo Diesel (soon to be "powered by VEGGIE") - dolphin silver

1999 e430 Sport blk/blk, my sexy ***** ;-)

(my other girls)
1992 300CE 24V 3.0L (w124) (R.I.P. "she was killed 7/12/03 by some ricer kids speeding in a honda accord")
1990 Acura Integra RS (w/94' engine)
1966 Cadillac Sedan de Ville (Hardtop)