Ideally you would need to measure the resistance in ohms as you move the flap through from closed to open.

As there are two it should be easy to work out which one is duff. Of course they both might be knackered or both might be ok. A difference between the two will show one is duff but which one I don't know.

Someone might know what the specification (resistance) is for these.

Also, shamless plug here but I'm flogging these ...