Fixed: I replaced the controller.
Here is how I determined that it was the controller that was causing the problem.
The broil element worked properly in broil mode. The bake element was not working properly, it got warm but not hot. The cycle lamp was on in broil mode and off in bake mode. This means that the part of the circuit that powers the lamp was not getting proper power in bake mode.
With the breaker off, I disconnected all of the connections to the controller and checked the continuity on the controller in broil mode and in bake mode. There was continuity in broil mode from leg 2 to point C, but not in bake mode. There should be continuity in each mode.
The controller is attached to the panel by two screws accessible from the outside of the panel, behind the control knob. The new controller is designed to replace several controllers of this type. It came with a long shaft with breakoff points and an adaptor kit with parts to fit the shaft to various style knobs. I had to break off part of the shaft to match my original controller.