Welcome to the site !!
I just looked thru the Factory Service Manual , as well as the parts Fiche and can't seem to locate it either , what it would appear to me is the notches would go over a spline , so i would be looking in the transmission or clutch for its location
You might PM (Private Message) Ken the owner here , its been a few years since i had a 250 apart and can't recognize that washer/bushing offhand , but i am sure he has had several 250's apart in the last few months and would most likely recognize it
That's about the best help i can offer at this point
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