I have an old dryer which has worked well until recently. It has begun blowing thermostats one at a time. I've replaced the high/low thermostat, the single thermostat twice and the ceramic disc thermostat twice. The fuse has not blown. The heater element tests okay. One wire end burned off on the singe thermostat at the beginning of this cycle. After replacing the thermostat the dryer will run for a couple of days (5-6 loads) before blowing again. The appliance parts guy says it is overheating and suggested checking for kinks or blockages in the vent. I did---there are none. Thanks,