The shop says I need a new pump but I see there are a lot of these o-rings on ebay. Is this o-ring failure common? If any have changed it one bolt holds the reservoir in place along with the )-rind as it slips the reservoir into the pump. If anyone has changed this o-ring how difficult/easy and a part number as I would think what you guys use is the same as what my MB needs. I want to try the o-ring before I change the pump. Thanks! Mark