Had the same problem on my 560 sel - drove me nuts for many months and several valve cover gaskets later - no cure. Problem? Warped valve cover! Put your valve cover minus gasket on a perfectly flat surface. If it can be rocked back and forth a little bit, it is warped. Overtightening the four cover bolts will warp these aluminum covers. Cure? Two choices. Buy new covers or do what I did - take the cover to a machine shop that can mill valve covers. They had to take off 7 mils from mine to get it flat again. Re-installed -MAKE SURE YOU DO NOT OVER TORQUE COVER BOLTS. Problem is gone. Cost was $70 Cdn. for the milling. Be sure to use new compession copper gaskets on the bolts when re-installing. Never over torque bolts - trust me!! Hope this helps. The puffing smoke is embarressing isn't it?