You won't necessarily see blue smoke or see oil on your spark plugs if the valve stem seals are worn. I had mine changed a few months ago when the head gasket was also replaced. Oil consumption went from about what yours is to maybe 1/2 qt. every 2000 miles.
A 30 yr. MB veteran at another MB web site once said that 103 motors are going to use a little. If they don't, somethings wrong. It's been my experience that European cars are not as oil tight as Asian cars. 1/2 qt. every 2000 sure beats 2 qts every 2000.
My 2 cents.