I have finally found myself a nice treadle machine. It is in near perfect condition, both the cabinet and the machine. BUT the outside of the machine is very dirty. Cleaning the wood was a breeze, but cleaning the body of the machine is a whole another ballgame. My husband and I tried everything that is non abrasive - from Windex to break cleaner to light oils. Windex seems to work the best but what I cannot understand is how much dirt is on it. No matter how much we clean it is still dirty - the residue on the paper towel is dark brown. Did anybody encounter this before? Are we doing something wrong? Help!