Being the cheapskate I am, I just used brass tubing from the local hobby shop. I forget the size, but, I took a bare shaft with me to find the size. Mine was worn enough that I didn't need to drill the base plate. I cut the tubing a little long, and carefully tapped it in with a small hammer and a piece of wood. I cleaned up the (inside) edge with a small rat tail file. Once the 'bushing' was in, I set the base plate on its side and put a few drops of loctite red around the bushing.
Its held up just fine in a real everyday driver situation and did away with that annoying whistle.