I have a 99 ML 320 with about 100K miles on it. The check engine light came on. I took it to my trusted independant mechanic and he reported the EGR passages are clogged. This delivers too much of the gases to cylinders 3 and 6 causing them to run rich (?) and triggering the check engine lamp.

He says he's repaired two other Mercedes engines with this problem. On one he had to remove the heads, on the other he didn't. He estimated repair bill at between $450 and $1800 depending on whether or not he had to remove the heads.

Is this common? Does it sound like he knows what he's doing? Is the repair estimate reasonable?

Thank you in advance.