Hemant .... You are in for a treat and lots of fun. It has been years so bear with me. The wiper motor I believe is behind/left of the glove box. It has a crank with a ball joint that moves a flat control rod to the driver's side wiper gearbox. There is a second flat rod that connects the driver's side to the passenger side wiper gearbox. The oscillation of the rods turn a gear that turns a gear on the wiper shaft that makes the wipers go. It sounds like you have a bad wiper gearbox. They are hard to see under the dash and harder still to replace. They are held on by two small bolts to keep them from turning and the main nut that is under the rubber wiper grommet on the cowl. By removing the wiper arm, chrome cover, rubber grommet and nut, you can unscrew the retainer and remove the wiper shaft with its gear. If that gear is stripped, you might get away with just finding a replacement shaft. Otherwise, I also recommend RainX.

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Jim Villers
190SL, 230SL 5-speed, 95 E320 Wagon, 01 E320 Wagon, MGB, Boxster 'S', 190SL "Barn Find"