Its easy to that $1600 is a lot of money, I can tell you that the labor for the repairs should have been 6 to 7 hours at whatever rate the shop charged. Dealers offer 1 year warranties for parts & labor. Most independent shops could offer rebuilt "air injection pumps" while Mercedes only offers new ones. That could have saved a few $$$.

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MERCEDES BENZ MASTER GUILD TECHNICIAN
ASE MASTER TECHNICIAN
27 YEARS M.B. TECH