Some of the newer pulleys are very poor quality. Don't skimp if you find one for less. Ray White sells them and I guess he tests them somehow. I can get them from my supplier but I don't anymore. The last one I installed ate itself in less than a day of use. There's an elna heirloom yahoo group and they have some sort of pulley they've created that's made of aluminum and uses rubber O-Rings for the contact spot with the handwheel. If I was going to change a pulley again, I'd probably go that route. That way if you get a flat spot, you can just change the O-Ring out and keep going.
The other things that help a new pulley stay round are to loosen the handwheel when the machine will be out of service for more than a week, and/or giving the handwheel a turn whenever you walk past it.
Lastly, you don't need a special puller tool to change the pulley. I can do it in about 2 minutes with a quick grip and a pair of pliers and a pin or with a punch.
The hook / two parts bobbin case in these machines are a challenge to disassemble to clean right, but once they're back together the machine does stitch very nicely. There's a video on YouTube that is a bunch of stills that can help a lot with this.