So you had the motor worked on by a shop.
Were the cylinder walls honed/bored over?
Was the block decked, cylinder head resurfaced?
What brand were the piston rings, valve seals, and headgasket?
Were the valve guides replaced in the head?
Is your motor clean, with no apparent leaks?
-maybe its running down your block from the VC in the back, and you cant see it
-It may also be leaking from the cam seals under the timing belt cover, running down, then dripping onto the header/burning off. This is what mine does.