Have you washed your car recently or has it been stood in anywhere damp, I had the same problem turned out that water gets down into the supposedly sealed motor and rots the connections.
I ended up having to strip it down and cleaning everything out, takes about an hour as you have to be very careful getting the body of the motor, flimsy plastic thing.
Clean it out and bung some silicon sealant around the join on the plastic body
Should be a good few years left it in it then.
P.S this does mean taking the Washer bottle out unless you have very small hands