I know this is a weak idea, but what gear oil are you using? It sounds like your syncros have seen some use. Try running some thinner synthetic oil, maybe that will help?
That's possible I guess, but I just don't understand why it worked perfect for 500 miles and then started slowly getting worse. I thought maybe the hydraulics were going bad and the clutch wasn't disengaging all the way, but that doesn't seem to be the problem. Is it possible the clutch disk is dragging the flywheel enough to cause this problem? There seems to be a bit of a step on the input shaft, but it isn't tight.
