My mom has a 98 E320, and my dad was going to replace to Oxygen sensor, is it located somewhere near the exhaust? I'm asking here for him. Thanks...

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1993 300D 2.5 Turbo
Daily Driver.... 238,000 miles and counting (Gone for an '03 Camry)
2000 ML-320
New Daily Driver...139,xxx and still in one piece...