had a look can't see a part number for it must be part of flywheel, I have one missing too from a flywheel but I have a dead flywheel so took it from there.
Looks like a thin wall tube maybe 19mm OD and 1mm wall, gearbox input shaft is 15mm dia.
I doubt it's the end of the world but if missing the felt ring could move, not sure if it's designed to keep the grease in the bearing for the bearing sake or the clutch sake, maybe both.
It is permanently pushed in you fit the felt ring before flywheel so it's trapped
