ok i have a t3/t4 turbo setup wit a 4an feed line and a 10an return but my return line keeps leaking oil and im trying to figure why?

Also a friend of mine has the same setup but his is smoking like crazy from the exhaust .it has a new head gasket any suggestions?

 

did u pin point where the leak is coming from? follow it and its either loose or sum kind of rip id think.