Sorry for the lack of response (feeling like poo at the moment :sad::sad
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The problem with most Mobitronic/Waeco product is that the crafty gits do not use the same pin configuration as the rest of the world. Sure you may find a monitor that has the same 5 pin Mini-Din socket as the camera/cable, but 99% will not have the same inputs/outputs matching the RV27 camera.
Don't rule out a faulty camera cable. My time working on a technical help-dest is that these cameras rarely used to create a fault, but monitors and cables were common (more so the cable as poor installation lead to cables "chaffing" on chassis metal etc). If humanly possible, try to unplug the camera cable and connect the camera direct to the monitor. If the fault has gone, ta da it's a cable and you do not have to use a Mobitronic cable as matching cables are available from other sources. However if the problem is still there, you could really do with someone near to try both items on their set-up.
Failing that, you can contact Dometic directly on 0844 6260133, then go to Warranty and repairs department. They may offer to test the equipment for you and quote repair/replacement costs.
Did try calling them to see if I could speak to someone whom I know that works there, but they are closed for Christmas.