Hello. I am new to the Mustang world and could use some help. I purchased a 96GT convertible from a friend for my daughter to drive to school. His father passed away and he collected them. He had about 15 cars and they would just sit in his yard. He would start them once a month. the mustang is stock and has about 90,000 miles. When I purchased it, the heater core was bypassed. I replaced it and then started having problems. The vehicle overheated and dumped all the coolant. I had it towed to the shop and they replaced the heater core/thermostat. A month later, the radiator and overflow cracked. Replaced both. Now, if I drive more than 30 miles round trip, i will park the car and about 45 minutes later, the coolant will overflow from the cap and I will lose about 1/2 gallon of coolant. The temp gauge will never go past the "A" in normal. The shop (national chain) can't figure out the problem. The have done 4 tests on the head gaskets and all came back "negative