Crank side coupler o-ring question

[Kohldanielzimmer]

So it appears later model 3 finger yamaha couplers have an O ring in the crankshaft coupler (part # 62T-45127-00-00). Mine is missing for some reason (see photo)


What gives? Do I really need this o ring considering prior couplers didn’t even have it?

 

[kevbo]

If the coupler bottoms inside then the rubber gasket just seals water out. All my aftermarket stuff bottoms at the base and uses a metal gasket. I often make gaskets thicker to help close up the coupler spacing. Those stock three finger couplers do occasionally break and can damage the mid shaft.