[V8] Antifreeze Sauna

[Mark Kalbskopf]

My car has had a dropping coolant level for some time, but I could  
never see any leak.
Tonight my daughter calls me 10 miles from home, pulled over and  
parked, saying that there's steam coming up inside the cabin and "it's  
stinky, and there's coolant dripping outside on the road."
The towing company want $140 so I go over there armed with 20 litres  
of antifreeze and various cans of water.
I clamp off the heater hoses and then drive sporadically home in a  
nerve wracking haze of antifreeze steam while willing the temp gauge  
to stay below 110.
All 10 miles there's a huge storm going on, so I think it helped me  
get home with the water splashing everywhere, but the windshield  
needed wiping inside every 10 seconds!
Anyway . . . .
What's the wisdom on what's going on here? How shall I spend the $140  
I just saved?
Do I have a broken heater core and how do I go about fixing it. (I  
have replaced the heater motor before so I'm familiar with that task.)

Mark
207,000 1990 V8