You took the car to a dealer and now you need a new pump? I've been a part of this community ten years, owned three Roadsters, never seen a pump go bad.

Sounds like typical dealer lack of diagnostic ability: "Its a complicated Mercedes system, we do not know anything about how it works, we don't know how to do diagnostics - so, lets throw expensive parts at it until it works".

I'd bet next month's rent that once you replace the parts, it still won't work. As you were asked above, what is it doing or not doing?

Read my sigline.