[CNHSS1]

As 30PSI says, probably an oil leak from the stainless braided oil feed hose from the block.
NOTE:- it isnt a nissan part, nor is the manifold, or oil return to sump pipe, they are all Scimitar items. Graham Walker or QRG will sort them if they need replacing.
Could well be the coolant banjos from the steel bundy pipes. They have a habit of the copper washers relaxing and weeping. Its generally microscopic amounts (as with the oil feed leaks) but makes a hell of a lot of steam/smoke!
If its water banjos, worth checking the 8mm return pipe back to the water header tank isnt blocked as the plastic header tank has a steel tube insert in it (to stop the jubilee clip crushing the plastic) that rusts up constricting flow and makes the cooling system prone to leaks.