1995S500W140, I'd agree with Brett on this one. We've both had water pumps seize with NO loss of coolant.
My car had run MB coolant for it's 11 years - there were absolutely NO signs on any corrosion on the water pump impeller or housing.
If you can do without the car for a while you should be able to find a specialist radiator shop that can replace the core of your radiator for cheaper than the cost of a new radiator. Also look around on the internet for a replacement waterpump. Sometimes you can find them for 1/4 of the dealer price.
As Miloking says check Jim Forgione's page:
K6JRF Auto Page
His 'Cool Harness' might be worth a try.