What's with the "IF"? Is the pump the cause or isn't it? He should only be replacing it IF it is the cause. Otherwise, he is replacing a part unnecessarily, at cost to you. Once a mechanic starts throwing parts at a problem, the repair bill starts to climb exponentially. Of course if you're okay with that then that's your decision.

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08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280