Your oil is going in invisible smoke at the back of the car.
Like the previous reply said, you are due for a valve job (guides/seals.) I just went through this routine 2 weeks ago on my 260E.This will also fix you oil leak as the head gasket will be replaced along with the front cover seal.
While you are there, have the timing belt checked. Mine was stretched quite a bit as the tensioner was at the limit
new plugs, distributor cap, rotor, wires and your good for an other 100,000mi
Good luck
JackD