I've repaired lots of those cameras. Check the bellows first, and if they pass, you can remove the front element by unscrewing 3 tiny screws on the focus ring and unscrewing the glass. From there, you can use lighter fluid to ease up the stuck shutter blades and if it continues to stay stuck, it could be a spring issue (which pretty much kills it). Once thing seem smooth again, open the back and use some fogged tape to act as a focusing screen and set you rangefinder on multiple object and adjust the front element accordingly and put the focusing ring back on. Also, don't forget to build a baseplate for the bottom since the tripod mount bulges and causes incredibly unstable support.