How do i know its' my heater core. I have a 95 chevy tahoe; fluid is leaking not from the core but from a hole at the firewall next to the hoses coming into the core. There are two hoses and one other with a rubber hose that bends at a 90 degree angle. After driving the truck and parking it, fluid leaks from this other (3rd) tube. Is it the heater core or something else?