Oil Leak from Lower Exhaust Studs

if you upload the picture , it will be more easy to reply and exact identification of causes.

This isn't mine but mine leak is identical. My engine is relatively new. 

Good picture.

This is seems to 4 possible  causes.

1. Engine stored for long times in downward position and after that when started some oil leak.

2. Worn oil rings may causes oil leakage

3.valve seals on inlet side only may be leaking.

4. Some of engine head with specific no have changed the parts .

Details in video.

https://www.rotax-owner.com/en/all-videos/free-videos/417-asb912062

Status of oil leakage?