To answer your question about the burner lighting off, then going out again, the spark ignitor, in addition to lighting the burner, acts as a flame proofer for the ignition module. When heated sufficiently, it send a signal to the module that indicates it's safe to open the gas valve.
Over time the ignition wire moves away from the flame due to the heating and cooling that it's subjected to. It finally reaches a point where the signal is to the module is too weak to keep the gas valve open. The solution is to gently bend the ignition wire back to it's original postion in the flame.
The model number you posted is not on Norcold's list, and we'll need to find the correct number should parts be needed. If you go to www.thetford.com, and select the RV tab,
you'll be give a list of their available models. Clicking on any of them will give you a photo of that model, and a description. By checking each model number, you should be able to find yours.
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