I have seen the pilot bushing come loose in the end of the crankshaft, which could also cause chatter. Oil on the disc is another.
Since you are going to have everything apart anyway, replace the disc for sure, and have the flywheel surfaced like Baldeagle suggested. Have the machine shop look at the pressure plate for you to see if it needs replacing or not. I typically replace everything when doing a complete rebuild just for the peace of mind. I hate doing things twice.
