I know nothing of cars but... Wipers are usually driven by one motor - one side of your wipers works - so the motor is working. One side of your wipers does not work so the linkage is likely jamming up. A bolt is missing - much easier to fit a new bolt than to waste money on a motor that you know is working.
On my Golf the wipers jammed - the motor's three mounting bolts had all worked loose - the motor was wobbling making the linkage jamb up - tightening the mounting bolts fixed the problem.
Seek advice from a another person who can examine the linkage - somebody who is not out to sell you something.
Peccavi
January 2011