This is usually an problem with the gas burner coils failing with age. A replacement kit is available (AP2150379) that comes with two new coils.

Let me see if I can better understand what you are saying. You replaced the coils, but sometimes when the igniter glows the gas never turns on? If the igniter cycles but no gas, then you could have a problem with a failing radiant sensor (AP2910747). It is a black box attached to the side of the burner housing. When the igniter reaches about 2200'F, it will open the circuit to the gas valves. It is also possible the igniter (AP3094138) is getting weak and not always getting to temperature, preventing the radiant sensor from opening the circuit. If the dryer was just dropping to 65'f without trying to ignite the burner, I would think you have a thermistor problem, but if it is trying to light but not igniting consistently, then I would stay in the area of the burner to look for the problem.

Yes it can. The entire assembly will come out of the cabinet for easier testing and to get a better look at the individual components.

The valve assembly can be taken apart, but I wouldn't do it myself. There is a possibility the seals wouln't seat back to the housing creating a possible gas leak.