Back doors

[Ray Austin]

On our mark 8 transit lwb rwb one of the back doors wont stay latched when open. The passenger side will lock after opening the door and using the sliding button and then wont move but the drivers side even if the sliding switch is used wont stay in the locked position but swing open into traffic if we are parked on the side of the road.

Any idea why and do they all do this before I take it apart.