I believe the engine in your car is the same type in my ML320. I have changed the water pump in mine. There is a DIY write up on it in case you decide to do it yourself or see for yourself what will be done by the mechanic. There is a special tool required. I found it on ebay. Since you are taking it to the dealership, I am sure they will use MB coolant. That would be the only recommendation I would make to anyone who decides to do it themselves. You could also use the equivalent zerex coolant if it is available in your area. The job itself took some time. If I remember correctly a couple of hours. Not exactly a ton of fun! Glad it is something that only needs to be done once in a great while. As to the belt, do you mean the serpentine belt? If so, I did change my belt when I changed the water pump. I had 105K miles when this was done, if I remember correctly.