I found out why my oil is going down so fast - it's leaking in to the gearbox. A common fault I've heard, netherless I'm a bit unsure on how to fix it.

I've taken off the oil injector pump and located a "seal" which I think is the one responsible for the oil leak, as well as two other O-rings. I'd decided to replace them all except the problem is locating the "seal". This seal has a 9.5mm inside diameter and no bearing shops or Honda dealer is able to find me a part number (even tried using this site) or a replacement that's even of an approximate size. Does anybody have any idea of where to locate a new seal? I'm in Australia.
_________________
MC21 Honda NSR250. TYGA 300 conversion.