Modern Vespa

74 small frame. Just noticed oil coming from rear hub seal. Put all new seals/bearing this past November. Was fine until now. I checked I have the right amount of gear oil (not over filled) and I just re-torqued the nut. Could this be anything else besides the seal? Also think it's ok to keep riding until winter?

Has the braking action from the rear gotten any weaker since you've seen this oil? Is there any oil on the other side of the wheel, coming out of the rear brake drum or along the rear brake plate?

If the rear seal is bad, the brake shoes would have oil on them and rear brakes would feel very weak.
This looks like a slightly loose rear axle nut and the oil made it's way between the rear hub and rear bearing inner race and migrated along the splines to where you are seeing it at the rear axle nut.

Hope this helps.