repairing old lenses or just opening them to clean has become a hobby of mine. Once I had scored a rather rare and to me also rather dear Voigtlaender Color Heliar SL f2.5/75mm, relatively cheap because it came in Canon breech mount.
I thought that one inner element might have a slight haze and decided to try cleaning it. It was a simple setting, me "on the road" in Asia sitting on a tiled floor, and there it happenend: An inner element fell out and on the floor and the glass chipped on one side!
Man, was I furious about myself and my stupidity! Since then I only open a lens if it really is necessary, and always use a soft surface to be working on, usually on top of a plastic plate that also would catch any small parts like screws falling out.
Resale value dropped considerably but now I shall keep it anyway. Luckily I can't detect any problems in performance! I guess because the chipped glass element is about in the middle of the lens. I guess it might lead to some reflections under certain circumstances. What do you think? Could it be that the chipped element really does not or hardly compromises performance?