other sensor, is for the solar sensor, to determine functions of the Aircon and climate system.
regards adding rain sensors, no mk1 is200 was fitted with them so, its not something that could be retrospectively fitted.
if there was a kit, then it could be possible...but i dont know, i personally dont have any issues with the intermittent settings.
regards the auto headlights feature, leaving it switched on, can cause the relay to burn out, causing the lights to stay on all the time.
so, i would only switch it to auto, during a trip, but switch it off, on parking