1981 kawasaki kz750e leaked oil.

Hi guys

I have a 1981 kz750e2 standard 4, I'm rebuilding. The bike is my father's but he left it sitting for 7 years. I took the project on and got to work. I used lots of advice from here and another site and managed to get it running really well and even legal on the road.
A few days ago I took the kz out for a longer ride in comparison to the little hops to the store and my father's house. Roughly 10 miles each way. On the way back it still ran fine but I notice a large amount of white smoke. I slowed down from 55 to 40 and it stopped.
I road to my father's house (because it was closer than mine) and stopped in front. I shifted to neutral and shut it off. I sat and looked down noticing a large amount of oil coming out from it looked like the oil filter shroud. I'd say less than a quart worth but more than I expected.
It started back up and got home (less than 2 miles away) and parked it.
In the 2 days since I've ridden it, it's leaked maybe a table spoon worth.
The filter shroud seems tight same with the drain plug. I'm having trouble finding the leak

Any one have any ideas why this would happen?

Could be a bad oring, or if you put in a new one it moved out of place during installation.

Pic?
Steve