Re: OIL in spark plugs holes
Assuming that this is residual oil.
It will take a loooooooooooong time for the oil in the plug holes to burn away. It's also inside the plug caps
Best bet is to clean up with degreaser - with the plugs in, plug holes and all the caps and everything in and around the plug rail. Wash out with water, redo with neat detergent, rinse thoroughly. Remove water and stuff down the holes to the plugs with a syringe/pump. Take all the plugs out, clean up everything you can without the obstructions. Pour some petrol down all of the holes, brush about, more petrol, spin the engine on the starter (HT leads well away - or - kaboom), clean up again, put plugs back in. Finished.
Or. Put up with the smell. It will go away eventually.
But - if it's not residual, it will be a leak on the gasket.
If so, new gasket and meticulous clean up or, old gasket, meticulous clean up and instant gasket on both sides.