Yes, check the "easy" things first! It could well be the centre crank seal, but it could also be something as simple as a broken/worn reed on the intake. Normally, when it's the centre seal, the bike will usually be hard to start, and often run badly at lower RPM. If it was the RHS pipe on an MC21 or MC28, it could be the RHS crank seal leaking additional transmission oil into the cylinder, but that would generally produce white smoke from the exhaust, but as it's MC18, the exhausts are routed differntly, and if it was the left crank seal, you'd almost certainly be drawing air and running lean.

Please keep us updated with your findings, as every shared experience helps the wider community.
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Andy.
NSR-WORLD.COM

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