turbo is smoking out the down pile

A little white smoke out the exhaust of my semi's usually ends up with oil all over the side of the sleeper.

IE the seal in the turbo is cracked and leaking oil into the exhaust side of the turbo.

If we idle the semi over night fuel will seep into the exhaust pipes and when the driver starts out after idling for the night the truck will leave white smoke out the exhaust.

So here's 2 idea's what could be the problem.
Fuel seeping or oil seal.

Marv