Primary/Secondary Switch

My GE microwave is intermittently blowing the internal 20 a fuse. The failure mode is after the microwave has completed its cycle, the power remains on; however, when i open the door, the fuse blows. I initially checked all the micro switches and they seem to work fine—again the problem is intermittent. Rather than replace all the switches, what switches should i consider replacing individually? Any advice is appreciated!