coolant loss at base of windshield 1984 380SE

Ladies and Gents,

I have a 1984 380SE (which I love) which has recently developed a coolant leak at the base of the windshield. Doesn't start until the car is warmed up and the bellows do their thing. Didn't leak hardly at all this summer, now it flows and causes steam (smells like coolant) to flow through the interior vents. Air conditioning worked fine this summer. I know there is an aux water pump and looks like some type of manifold or valving there, but not what else.

Dealer says it is the heater core and will be $2500-3000 (lot's of labor) Any ideas before I spend this amount, it may be cheaper to find another car? They did sya it might be the aux water pump, but doubted it. There is no visible coolant in the interior (other than the steam smell)

Thanks
dave dabay