mdawson, I had that exact same problem with my 84 500SEL. Idleing or going slow down hills, and then accelerating it would create a cloud so bad you couldn't see the cars behind you but other wise it used very little oil. This is what I found.
I removed the left (drivers side) valve cover. The cam oil tube mount at the rear of the engine was broken. Just above that spot is where the PCV system gets the fumes from the engine. Oil was spraying out of this broken mount directly into the this PCV port, running DOWN the channel in the top of the valve cover and right into the PCV hose. The fix was to replace the plastic mounts for the cam oiler tubes. I would go ahead and do both sides if you find they are dark brown in color. New ones are white.

PaulM

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84 500 SEL (307,xxx miles)