Bob, it does seem unlikely, but we couldn't think of any other way for several pinholes to get in the shutter. This was discovered in December 1965, at Jack's Camera in Rapid City SD. The shop had two large west-facing "picture windows" on either side of the front door. There was a low platform to elevate the display items above floor level, and typically the cameras were tilted lens-up for easier examination by passers-by. It was part of my job to keep the display tidy and to wash the windows each morning.
Some of these cameras sat there for months. For some reason several Kodak Pony cameras stick in my mind, both 35mm and 828! Not much buyer interest in those. Anyway, I expect that day after day (especially near Summer Solstice) the afternoon sun would pass about the same track, and be focussed on about the same area of the shutter. Evidently enough of this repeated heating of certain spots burnt several holes in the shutter. I wouldn't be suprised if there were other thin spots that hadn't yet burnt all the way through.
I enjoyed taking out various used cameras to try, and it was in using this Nikon S2 from the shop that we discovered the pinholes. Only focal-plane shutter RF cameras would be vulnerable. One other such I borrowed was a Canon Vt (with trigger winder); not sure if it was from the window display but if so it may have been "saved" by different positioning.
Say, the old Contax and Kiev RF cameras had black-painted brass "roll-top" shutters, didn't they? Low melting point, easily oxidized... What did Nikon use?
Doug