I have a '96 850 GLT, non-turbo motor, with a problem. While a friend
was behind me driving it home for me one night, all of a sudden, I
noticed in the rear view mrror that he had completely disappeared within
the cabin in a cloud of steam. It turned out (or appeared to, anyway)
that the heater core on the passenger's side burst, releasing vapor into
the car.

The red warning light for low coolant came on, but we were able to limp
it back to my place abou 8 miles away. Later, I refilled the coolant
reservoir, but it steadily leaks out from somewhere under the car.
Though the steam inside the car was readily apparent that evening, I
have yet to see any evidence of water inside the car. Rather, it seems
to leak from along the side sill under the car on the passenger side.

What gives? Any ideas as to where the leak really is?

Thanks in advance for any advice.