Winogrand's last M4 is a historical artifact and museum piece, not a camera any of us own or have inspected, or should be wiping alcohol on. The likely source of the markings is the film base reacting with and pressing on the finish of the pressure plate, not the film base actually denting metal.
However, I haven't seen old moldy film make a mark on the pressure plate. I have seen it react with and put corrosion on the film rails. It is more likely for the emulsion side to get moldy or react, than for the base side, which is just plastic. So I'm willing to believe that the camera was worn from use, not storage. Stephen Gandy's page shows that the camera has a lot of other wear from heavy use, and that the owner after Winogrand was actively using it, not storing it. And Gandy physically inspected the camera, which we have not.
Some cameras are much more regular about aligning the sprocket holes with the film always in the same place, so that even as the film is advanced the sprocket holes always come into the same place with respect to the frame, as likely happened here. For a long time I had just two 35mm cameras in use and I could tell which camera a negative strip came from by the frame spacing (they were a Nikon F and a Canonet, and of course the F was more regular, but that isn't a knock on the Canonet, the F was built to a more solid standard and weighed like it).
I also do not know if all 35mm cameras have the sprocket holes detented to a specific position with respect to the frame. Obviously many do, but there may be some where it depends on where you start the film.
) but if held at the right angle to the light it too distinctly shows a faint wear image on the surface of the pressure plate - essentially a difference of reflectance that allows you to see where the image area is and to differentiate that from the area where the sprockets are. I can't see any image of individual sprockets, but I can clearly tell where the film rails are in relation to the pressure plate.
