So this is about my 96 GMC 1500, but it's related since it also has the 4.3. Anyway, it applies to just about any GM truck. So. I am a fervent believer in dumping, flushing and cleaning out DEXCOOL. Hate the stuff. Every vehicle I've had that has had it in I have promptly done the DEXCOOL clean for green. Well my dad tried to do it to the GMC but didn't do it right. There was still gunk in the radiator and the heater core. SO bad I had to replace the radiator. Took a half hour to flush the heater core clean. Well when I did that I simply disconnected the quick connect and the other hose and flushed it through there. But before that I'd had a constant, slow coolant leak. But couldn't find it. Shoulda known. SO i put the hoses back on and refilled with green. Drove to work the next day. OK then I get home and check the engine. Now I also had to replace the water outlet as that broke (old) THought that WAS the leak. Uh uh. That was dry but I was hearing the high pitched teapot whistle. I thought it was the outlet but as I listened it was coming from the side, not the middle. Sure, the damn quick connect was leaking. Now this is the 4th GM engine I have taken that damn thing out and put in a regular nipple/hose clamp setup. NO MORE LEAKS. which is good as it's gotten cold and having heat is much appreciated. I have now done that on 3 4.3's and a v8 in my old Tahoe. SHoulda checked that first. Easy fix as long as you get the right nipple. It's important to get one with the restricted flow otherwise you can blow the heater core with the full pressure from the engine. I just kick myself for not having checked that first.