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.
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MC21 Honda NSR250. TYGA 300 conversion.

Hey mate
Generally, the seal is reused with a little bit of sealant.

The genuine part number will be in the parts manual.
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Winning isn't everything, but loosing isn't anything

What sort of sealant is appropriate? I couldn't order the part from honda, despite finding a part number, not sure if it was the correct part number either, as they couldn't find it on their computer.
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MC21 Honda NSR250. TYGA 300 conversion.

The search function is your friend:

"oil pump seal"
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MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball

Hey mate.
You wont find a Honda dealer in aust that will be able to help you with it.
Try online. Tyga might have them.
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Winning isn't everything, but loosing isn't anything