I picked this up at an estate sale. I am trying to determine whether it's gold filled. There is no wear on the bezel or front of the case (the caseback is SS) suggesting it is more than plated (or it could be a heavy plating). Where would I find a marking that says it's gold filled? By the way, it runs and the quick date set works great. It says "waterproof" so I am inferring it was made before 1972.