I recently acquired a Zeiss Ikon Super Ikonta 533/16 folding rangefinder camera in very good shape. The only fault was the very stiff focusing ring. When repairing that I took the front metal ring off, by unscrewing the three little screws on the sides.
That is a tough one and it really depends on a lot of varibles. If the scratch is in an area where there is enough metal that you can work the surface down to the depth of the scratch and re ploish your in luck auto body supply shops and some auto detail