I think I split 4x362 and one 372 last months, 50% of them had the o ring the rest didnt have it. They are all 00-03 models and for that reason I study the IPL close, else I would probleby over seen the whole ring.
I just had a 365 apart and if I had not been reading about this o ring on that other site I would never have known there was one, all I found was the remains was a bit of black residue between the bearing & the crank.
When the clutch is tightened against the sleeve it squishes that little o ring against the bearing sealing between the sleeve & the crank, but it squeezes the o ring to oblivion.
I've built more than a few without the oring...doesn't seem to be an issue. I don't know why not....but its not. I'd rather use it, but if you don't have one, I'd put some 515 or 518 on the inside of the bushing and just go for it