I've got a GE CGS990 gas oven that's been working well for the past year.
On sunday (of course) the bottom oven stopped getting hot; I took it apart and found the ignitor was clearly broken (small crack). The broken part is probably a generic part -- it had ceramic wire nuts attaching it to the oven's wiring.
Today I replaced the ignitor with a generic unit from the repair shop down the street. Both are flat looking ignitor elements. The cranky old man at the shop assured me they were all the same (ignitors, and possibly cranky old men who run appliance repair shops).
I replaced it and (foolishly) put the oven back together.
When I turned the oven on, I could see the glow of the ignitor, then the gas valve opened and the burners came on; after about 45 - 60 seconds, the glow got brighter and brighter and turned from orange to white, then there was a popping sound and the oven turned off the gas flow. The new ignitor was broken in two places; nothing else looked amiss so I don't think there were any shorts or other issues with the replacement.
At this point, I'm not sure if I should throw another ignitor at the problem or call in a professional. I'm not sure if the different ignitors are actually the same or if there are differences beyond the mounting bracket and connectors.