I would add to my previous post that the operation of moving the bumper
holder MUST be done with the disk
at full rotating speed.
In fact, this will move the head, that must fly on the disk surface.
When done with halted disk, the head movement could cause severe damages.
PS - BTW if somebody has a great amount of these disks to be repaired,
I would be glad to have some for my DEC machines here.
Andrea