Product review (5 stars): Genuine Norton 501A Ignitor
I wasn't sure if this would be an exact replacement for a Maytag 12400035, but we needed 3-4 of these and the price was right.  When they came in they bore a tag saying they were Norton 501A, same as the Maytag, so it's hard to go wrong with these.

The one difference is that these don't have a plug connector, just stripped wire leads.  I clipped off our old unit below the plug and used the wirenuts supplied to connect the replacement to the clipped leads, keeping the plug there just in case.

Both the bake and broil ignitor that I replaced today worked perfectly the first time and started gas flow in under a minute.  The only hitch I had was stripping the threads on one of the two screws holding the ignitor on the bracket.  I found out it's easier to take the whole L-shaped broiler burner tube (it's held by one screw at the front), clip the old ignitor leads, then pull it all out and work on it outside the oven.  The mounting screw is a 10-24, and I had to go get my own replacement (stainless for high heat, although I don't know if that's necessary).

At this price it was worth it just to replace all the ignitors at once, and the oven seems much better.