Well, I looked for some of the items that you mentioned but only as a cursory look before cleaning. This morning I gave the thing a wind and noticed that, when rotated 180 deg. between DU, DD, and then DU again, I could hear what sounded like something falling into (or out of place) – this was accompanied with the “ringing” sound in the DU position which leads me to believe that the end play might not be right with the balance staff. However, it could just as easily be one or more of the possibilities that you listed. So, I suppose my weekend will be full trying to systematically determine and fix the problem.
First I think I’ll take out the balance and see if I can get the bottom cap jewel out without taking the main plate off (It’s a full plate so that’s a pain) to determine how far the pivot extends into the hole jewel. Since the problem is predominantly occurring in the DU position, it seems like the balance jewels are a good place to start. If I can’t see it there, then I’ll move on into the other areas.
I’m ordering a Ace Timegraph this week so that might help a little.