The problem is a finicky ignition system, Direct Spark Ignition. Apparently Whirlpool redesigned the igniter/burner assembly slightly to make it more reliable. The repair is very easy. Turn off power, but you don't need to turn off gas. Remove oven bottom and flame spreader, then remove burner/igniter assembly, one screw at front, one at back. Lift out burner assembly carefully to avoid stretching wire. Pull electric connector from pin on burner/igniter assembly. Vacuum to clean oven. Attach electric connector to new assembly, lower burner assembly and make sure it is properly aligned with gas outlet. Reassemble remaining parts. (I installed a new oven bottom too.) I won't know whether the oven is completely reliable for some time, but it looks promising.