I was enamored of Yashicas for a while. I had a stack of them, including two fully functional Lynx 14e models. There was a guy in Arizona who used to make a working battery adaptor for the Yashi's with the big battery in the back. He sawed off a 410 shotgun shell just above the base cap and used a correct voltage contemporary silver oxide battery. Worked great.... use expired shotgun shells, please.
Back to your question. These camera's were so cheap and plentiful that I used to bring the sticky ones back to life with the proverbial "Ronsonol Flush". Ronsonol lighter fluid judiciously applied through various openings in the lens rings. Exercise the lens aperture and shutter greatly while the fluid is still wet. It flashes off fairly rapidly, washing out the old hard grease. It didn't work all the time, but it worked more than half the time. I've used it successfully on Olympus rangefinders (The 10 and 20 dollar ones), and other shutters, including large format.
Now, having said that, Please, Please, Please don't do that on your Leicas, any digital cameras, or other rare or pricey cameras. However, don't be surprised if that's what your favorite, $600 for a CLA, service person uses to limber up your apertures and shutters first before tearing into the inner workings.
Disclosure.... I only offer this suggestion for camera's you are going to throw away if they don't start working.