I just replaced my heater core last month... It is working really well. The problem is that we had a hot day when I was testing the heater output. Everything works perfectly. I got it a bit warm in the car, so I shut off the heater and opened the upper astro vent.... The dang knob came off in my hand AGAIN! I think that I am going to use the chrome handle and fabricate my own cable... It has to work better than these! It just looks like they aren't pressed on very well. I may try to thread the inside of the knob or maybe try to add a set screw from the side.... Any ideas?