Report : As per instructions I dismantlet the Isolette top and was able to get at the little rangefinder wheel without too much difficulty. I screwed out the rangefinder wheel, and discovered the cause for the distress.
The grease ahd turned green-gray over the years, and firmly glued the wheel to its base when fully screwed in.
As and old shooter and old gun collector I'm very familiar with this stuff, we call that verdi-gris, it consists of fats and corroded coppers from the bronze.
Luckily shooters have an effective remedy : it's called Hoppe's No.9 and can be found in any hunting store all across the globe, or the people there WILL know what you're after and offer a substitute.
This stoff is formulated to dissolve copper deposits and leave the metal clean, and this was what I used.
Used a tooth-pick to get out pesky remains and after that screwed the wheel back in to ascertain that everything did function, them took it out and greased it.
It now runs freely, I just need to go back in and re-calibrate the rangefinder. Seems I now have a fully working camera!