I have done fuel system work on caterpillar diesels for 14 years now and some poeple will tell you that they will "rebuild" a fuel system and all they will do is throw new gaskets and seals at it. And some of these rebuild prices seem low. Keep in mind that they can't give you a solid quote untill the pump is totally disassembled and they can see how many parts they need to replace. At which time it might be more expensive to rebuild than get an exchange. Here is another piece of advice. If you have a fuel system "shop" rebuild your pump, will thier warranty cover a repair in another state? Doubt it. If you get a "factory rebuild" the warranty is covered at any Mercedes dealer. Very nice when your a 1000 miles from home!! Plus wouldn't you rather have a factory pump instead?