Hi Mike - Both times I took the seals off- the bottoms were flat with no markings indicating a possible oil leak. I had used an aftermarket gasket that was slightly wider and I thought that was it - so I got a genuine Mercedes gasket and put it on last night. After the initial burn off from the oil that leaked onto the exhaust which took about 20 minutes - there was no smoke - until I held the engine at about 2000 rpm for about 15 seconds - then the big plume came up from the passenger rear area of the motor. Wait a couple of minutes and the smoke stops - rev it up and - whoosh - there she is again. I always thought it was the gasket as there is a bolt that holds the tranny filler pipe at the rear of the engine just below the top of the head - sort of looks like it is screwed into the back of the head with the cover on - that I dried off and found it was wet again after about 100 miles. That is why I suspected the valve cover gasket all along. However - the first gasket was in the car for about a year and the first time I drove the car last year - when it hit operating temperature - that is when the first plume of smoke appeared. It only happens once the engine is at aoperating temp. - when the engine is cold - you can rev it up and it won't smoke - only when hot. That is why I thought the rear sealing edge of the gasket was not catching completely on the head. So I loosened the 4 bolts and pushed the valve cover gasket forward and upward as far as the bolts would allow and then tightened them. - Same thing. I too use a 1/4 drive so I won't overtighten them. When I went right under the car last night and looked up with a light - the whole rear passenger side of the motor was dripping wet with oil from somewhere up high - the only two things I can think of are - valve cover gasket or another plug leaking - if there is one. Without pulling the exhaust - it is a crap shoot - but I am afraid of broken studs - If all else fails - I will have to bite the bullet and pull it to get to the bottom of it. The only other thing I can think of is a slight crack in the valve cover that is not easily visible when cold and expands enough when hot that the splashing oil under the cover can leak out through. Everyone I have talked too have never heard of this happening - you can't get to the rear of the cover low down to check for oil.
If Dave sends a pix of the rear passenger side of the engine - it might be enlightening.