strange rh crank o ring set up?

[asshat]

Hi all.

Me and a buddy are into a complete rebuild of a 01 ec 200. The crank main drive gear is put on with a cir-clip, and there is a bushing which the seal rides on to create seal. on all gasgas i am familiar with (have 2 an 02 xc 250 and txt 280) and according to the only manual circulating currently, the oring goes against the crank, then bushing, then tighten nut against drive sprocket. which creates seal. This one however looks like there is a groove in the crank, which you slide a thin o ring into then slide bushing over so o ring is actually inside of bushing. Has anyone seen or is familiar with this setup? is it 200 based or year based? or am i out of my mind. in ordering parts we got an o ring which is far to big to go into the bushing, looks like its the o ring for later style engines with nutted cranks (have no year based parts catalog only a 2000 and a 2003 which are clearly different.) there is clearly o ring marks inside of bushing, and it looks like at some point in its life the bushing was flipped because it has symmetrical polished marks inside of bush. I did not take engine apart and have no year specific breakdown, and manual i have is the generic one size fits all one everyone seems to have.
So is there actually a different thin oring which rides IN bushing? Has anyone seen this?
Help me please i have been staring at it for a couple of hours and all the info i have read mentions nothing of the type of seal.

any help is greatly appreciated

thanks
Asshat