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.
Car Problem Reports
Cadillac Escalade Quick-Connect Fittings For Heater Hoses May Leak Engine Coolant
Cadillac Escalade Problem
Visitor, 2005 Cadillac Escalade, 150,000 mi
After repeatedly needing to refill the coolant reservoir, looked for the source and easily found traces of coolant on transmission oil filler tube, directly below the quick connect fitting on coolant line going through firewall. The tee connector needed to be replaced.