Douglas,
The wiper motor on my '70 280SL (# 15,xxx) is bare metal (silver), base inclusive. It is mounted to the body with three cad-plated socket head cap screws.
An interesting thing to note is that mine does not have any torque stripe markings on the 2 flat head machine screws located on top of the cylindrical section. This contradicts the blue torque stripe markings I saw on Hatch & Sons’ restored 280SL shown at Starfest. However, I've never seen torque stripes on any other 113's wiper motor screws--the professionally restored examples go a little overboard with the torque striping.