The quick-connect fittings for the heater hoses tend to leak engine coolant. This problem commonly occurs because the metal housing has become brittle, which can break and cause leaks.Google+
Car Problem Reports
GMC Yukon Quick-Connect Fittings For Heater Hoses May Leak Engine Coolant
GMC Yukon Problem
Average Mileage: 155,400 mi (55,000 mi - 283,000 mi)
Visitor, 1996 GMC Yukon, 55,000 mi
I have had the connector replaced by a GM mechanic twice in three years. I bought(4) connector none stopped the leak. I then went to the repair site and the info given states to replace the connector with a threaded hose connector from Advance Auto Parts. Will ask for this part at Advance Auto Parts.
Visitor, 1995 GMC Yukon, 168,000 mi
broke off poor design
Visitor, 1996 GMC Yukon, 121,000 mi
Heater hose connector leaked and eventually broke off.
Visitor, 1997 GMC Yukon, 150,000 mi
fitting broke off,