I know for the 6-cyl M104, the EGR tube resides behind the engine. And it's buried! Which is why you mechanic said what he did.

My indy had the head off on mine for a new gasket and didn't check the EGR when it was readily accessible. Later on, the car didn't pass smog because of the clogged tube. He cleaned it with a makeshift pipe cleaner with a long stem, but admitted it would have been far easier to do when you could actually get to the tube.

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2009 ML350 (106K) - Family vehicle
2001 CLK430 Cabriolet (80K) - Wife's car
2005 BMW 645CI (138K) - My daily driver
2016 Mustang (32K) - Daughter's car