hydrolic fan pump pulley?

I have a 2000 lincoln ls 3.9 I have had a noise coming from one of my pulleys for a while now. iv replaced the water pump, both idler pulleys, and the tensioner. It still makes the noise, It dosn't happen when the belts off. Based on the pulley diagram, Rod sent me in my last post, I have located the hydrollic fan pump pulley and am pretty sure it is the cause of the noise. When i spin it, it gose half way around and it stops, It rotates all the way but not smoothley. Is this hard to change out? What is required? Also any ideas where to get one they want 260.00 at the dealer just for the part.