Thanks guys for all your comments .I have solved the riddle.

I had earlier noticed a hissing sound while driving , all along i thot it was the wind blowing thru the small aperture i leave open with my door windows whilst driving. So i parked the car in my garage one evening so as to check for the vacuum valve you guys spoke about and found out that with the engine idling away, the hissing sound continued just behind the Fuse box area . On searching the area i found a tube blowing air had come loose . Picked it up and searched the area for the most likely place to stick it in and saw a kinda y-tubing going all the way in to dash console in the car. So i just stuck the tube back in to the y-shaped tube and voila! My indicator starts working again.

once again you guys have proved very helpful. Thanks

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1986 230E (revisions on the way)