If you go to an industrial supply store they will have a life size chart which you can lay the seal on to match O.D. and dia. of rubber. Even if you have to buy a quantity it will be cheap.
Thats the plan. But the orings are busted. Im sure Ill find one that fits via an oring chart. However it would be easier to order knowing the correct original the size.
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me: '76 Claus Bang
my girls:
'93 Ducati 900 Supersport
'76 Honda CB750 K6