I always thought the gray/white crusty deposits were from running too hot or too lean in the combustion chamber. If too lean then you may want to adjust your fuel/air mixture. If too hot then you might want to go back to the standard and cooler W8DC plugs and see how they look after a few hundred miles.
About the burning oil, do you get smoke out the tail pipe? How much, what color, and under what conditions?
Rodd
Powell, Ohio, USA
1966 230SL, Euro, Auto, Leather, both tops
1994 E420