If you see fogging in your rigid Summicron, I would have cleaned it up.
All these old rigid and collapsible Summicons have haze more or less, if not cleaned before.
I am not 100% sure, but I think, the haze comes from an grease/oil that Leica used back then. The grease usually spreads over the aperture blades and dries. Within this process of drying and deteriorating, the lens surface (mostly the one underneath the blades) becomes hazy.
If you don't have it cleaned, the process remains, and the lens will get more foggy sooner or later. The earlier this is cleaned, the better, if you wait, the fog could go into another inner surface (within the elements) and then you will have a real problem.
But be sure, the repairmen cleans the blades and everything else, like the helicoil also, because, if he cleans the lens surface only, you will have it fogged in about 2 years or so again.
Hope this helps with your decision.