not sure if the cranks is same as 1989 ?? but I found a pic on google image of a '89 crank fiche/diagram. shows centre bearing koyo 68od x 28id x 19 part no (83c137ejh2-9tcs39) and centre bearing seal Honda 67 x 1 part no (91301-kv3-771).
The seal is available from fowlers parts.co.uk £1.51 +vat postage etc.. hope so as this post has me worried, I'm just about to buy a low mile mc18