^^I will definitely keep you posted, I don't know too much either, but I've asked around LGT/WRX/STI Manual Gearbox owners, even had a few drive the car to understand my rantings. I think the pumping of the pedal may be resulting in shifting the fork slightly (when you depress and let off) from the position in which it vibrates. For me I have noticed that when it is vibrating pressing it lightly sometimes eases or stops the vibrations completely, this is why I am hoping I am right (or at least on the right track) with the issue being realted to the position of the fork.
Also, I have the aftermarket TOB above, and unless the bearing itself has gone bad, then I dont think this is the cause. There are 2 pins on the TOB that lock it in place on the quill, so when the clutch is engaged, it moves with the fork.