You should stop taking the car to some fool who is not checking to be sure the pump is getting power.

I strongly suspect the issue is a weak/bad relay in the RCM, if you replace the RCM you will know if that is the issue. You can buy an RCM for $130-180 from various suppliers and replace it yourself without tools. They literally plug right in; you need NO TOOLS or skills to replace one, just pull ONLY on the connectors and not on the WIRES themselves and you are fine.
You can't even plug the wires in wrong because all the plugs are different sizes!

Its super easy.

You want the "Relay control module" for a 2003 Mercedes SLK320. You can say "Crossfire" but often, the price is higher for the SAME PART.