I know this may sound like a bunch of hooey, but it's best to use the original setup when replacing these heater hoses and fittings. The quick-connect fitting that taps into the intake manifold has a certain amount of restriction that the system needs to get just the right amount of circulation. (I'm told that...) Too much flow contributes to blown heater cores.
When you replace that quick-connect fitting you don't have to worry about it breaking off like the factory-original part because every replacement I've seen is made of better materials than the pot metal that GM originally used.
