[slammera]

The door release appears to be non-operable, in other words it just pushes in with no resistance. This occurred when trying to open the door and resulted in the machine turning on. The stop button did not turn it off and the door would not open. The only way to stop the microwave was to pull the plug.

What is the problem and is it worth fixing at this age?

Door will not open.
Powers on and will not stop via touch pad.

[Gene]

Most likely the problem is a broken latch spring inside the door. The door is not serviceable and the correction is to replace the whole door. Unfortunately this part is no longer available.

Gene.

[MicrowaveDisplaycom]

I believe you instead have a broken door release lever, which is not inside the door.

It is part # WB6X452, ref # 2006 on the helpful exploded view diagram found here.

This part is still available here.

The outer cover of the oven will need to be removed to diagnose and repair this.

Please unplug the oven first.

Once the cover is off, you'll be able to see how the door open button should press against the door open lever, which would in turn lift up against the door latch heads (hook-like projections on the door) and then the door should open.

Usually one of the "nubs" breaks off, allowing the lever to drop out of the mounting / guide holes. Then the lever can't pivot anymore.