Modern Vespa

What could be causing this? Any ideas? Rear hub? Clutch breather?

sure looks like your hub seal to me, need to get that hub off and have a look.

your brakes will go to shit if they haven't already.

I bet it's residual oil from Ned's sidecar clutch cover vent leak. Were you riding directly behind him at ROM?


Also, the rear brake cable clamp looks a bit concerning to me...

Hard chuckle.
Maybe.

Chatis - it's one of two issues.
1. Rear main shaft/axle seal.
2. Breather on top of clutch cover

a bore scope can be snaked up on top of the motor to se if it's the breather - but assuming u don't have one - next best thing is probably to pull the wheel off and do a visual inspection.

You will find a trail from where ever it's coming from.

Don't forget the cotter pin…

I have/had the same problem. In one of the engine I had a bad clutch cover seal. on the other one I haven't touched it yet but it is annoying. I also laid down my scooters many times recently swapping cylinder kits and exhaust for testing, I wouldn't be surprise if I cause some of the issues. Also, some exhaust leaks more than others, I found the undercarriage greasy and all the saturated oil from the exhaust typically drips to the very bottom and concentrate.