Passenger wiper arm doesn't Move

A few days ago it stormed and I noticed the blades were dragging and being loud. Prior to the storm, I had new blades put on two weeks ago, so I knew it wasn't old blades.

Today I cleaned the blades with alcohol and tightened the passenger nut. This didn't stop the passenger from dragging. The drivers side is great. I loosened the nut a little just in case if I over tightened. I turned the wipers on and the passenger arm stopped moving. It tries to but won't. So I took the arm off and turned the wipers on. The stud or whatever it is it sits on moves perfectly. I put the arm on again, and it tries to move but no dice.

So I went to a junk yard to get another arm. Got it home and it's for the drivers side. Researched a little more and saw to clean the teeth of the thing the arm sits on. Done that, put the passenger arm on and same result.

Called a parts house and explained to him the problem. He asked if it has teeth on it. I said yes but the arm itself is smooth inside. He said I need a new wiper arm because over time the teeth have worn the arm smooth.

So, what's the verdict? New arm or something worse?