Back in 1974 I sent a early chrome M3 back to the factory to have it made in black. I just wanted a black body I was not a collector (1) and had no idea that they were rare. It came back in four weeks sealed in a plastic bag just like a new camera and looked that way. The next year I had my chrome M3 overhauled and redone, I still have the chrome one and it looks great. So it could have been done after the fact, anything was possible then and the only difference if it went thru the repair dept. was the L seal was different. I forgot which way was which but one was raised and one sunken. Let's be honest any Leica with a intact factory L seal is way overdue for a complete overhaul. Back then it cost about 300.00 dollars to have it done, and the camera had a new rangefinder installed, shutter, top and bottom plates you could not tell it from a new camera.
wbill
