Belling cooker - oven dial slipping

It's as if the external dial isn't properly catching whatever it is actually turns the temperature up or down. Very annoying - initially it meant that the oven wasn't actually 'off' at 12 O'clock and we needed to go back to 10ish, or that what we thought was 180C was actually 150 or so. Now it doesn't seem to go off at all and we need to use the mains switch.

Does anyone know if there is an easy remedy to this - e.g. if I attempt to remove the dial and have a look will it be difficult to get back on?

Thanks