2005 Mazda RX8 Cooling system

I have an '05 mazda rx8. A few months ago my heat quit working. I had the heater core flushed at a shop and the heat worked for about a week then quit again. After that I decided to flush it myself. I flushed several times but have never got it working very well. Passenger side blows warm but driver side blows cool. After several flushes and then just giving up I recently noticed that I'm losing coolant. I can smell coolant through the vents but couldn't find a leak. No signs of the heater core leaking either. Today I decided to investigate further. I filled the reservoir up and let it warm up for a while then I revved it up for a while and it started steaming bad. I shut the car off and opened the hood and seen that a lot of coolant had leaked out onto the garage floor. I couldn't find the leak so I took the reservoir off to get a better view and when I did I noticed that the overflow was broke off from the radiator. Not sure if I did this or if it was already broke. I'm willing to get another radiator but I was wondering if this was my problem all along or if I just created another one. I really just want to get it fixed so I can sale it