my new 80cc motor looks like it's leaking gear oil.

might be that your case bolts aren't tight - use a hand impact drive to tighten them up

if you can, tighten the three under the clutch

Have not seen it in a while but then again I dont build as much as I used to. Sometimes the factory will stuff the bearings with grease.

I was told by a supplier in China that the reason is the motors would lay on their side in the box for so long the bearings would dry up and fail. So they started greasing them during assembly.

Years ago every kit I built would have a little grease come out but usually dissipate after a short time. Maybe this is also the case with yours?

I over-greased my clutch-axle chamber once, and saw the same result: grease seeping past the right bearing and appearing behind the clutch-plate. It wasn't enough to contaminate the pads, and stopped soon afterwards. I don't see it as a problem unless the pads are getting affected.