Hi all, yesterday it was raining heavily,and i had to take my car out, i used the wiper which seems to take its time to sweep off the water droplets on the windscreen,the way it swept didn't seem normal to me, it was struggling to return back to its position and at one point just got stuck half way,and i can hear the motor run its not able to get back !! i would appreciate some help and suggestions.

Model : w124, 1987 300D

Thank you !!