I am going on the mechanic's report from the dealer. Do not know how they test the coolant system for leaks.

The report says coolant is pouring out and should be towed from the dealership if not repaired. I'm sure this is CYA

Right now I use about 1/2 litre of water per trip and a few hours of being parked. I just fill the res and go. I know I'm on borrowed time while I put the money together.

Parts prices from non Mercedes suppliers seem to be less than $400.

When I was young, 60's and 70's, I had a similar problem and lasted for quite a while. I'm concerned about a quick disintegration of the pump.