Fuel Filler Door

Like others before me, my fuel flap door very intermittently fails to unlock (i.e.via the central locking). So far, it has always opened on the second operation of the central locking.

The motor locking unit is expensive it think (£100+?). Has anyone dismantled/oiled the unit successfully? There is no question of my unit not being powered to open, it just doesn't always allow the catch to disengage fully.

I am uncertain of  oiling it when there will be a commutator and brushes to be wrecked if it ends up in the wrong place.

I notice that there is no drain hole on it's plastic case, so eventually it will fill with water/crud, won't it?

Cheers.