Great cameras and I second Jon's light seal kits. I have been using his kits since 2008, great instructions and fast to ship. And my only connection with Jon is a happy customer.
“Every gun that is made, every warship launched, every rocket fired signifies in the final sense, a theft from those who hunger and are not fed, those who are cold and are not clothed. This world in arms is not spending money alone. It is spending the sweat of its laborers, the genius of its scientists, the hopes of its children. This is not a way of life at all in any true sense. Under the clouds of war, it is humanity hanging on a cross of iron.”
― Dwight D. Eisenhower
Earlier this week, I replaced the light seals on my k1000 and my yashica. I used the black yarn technique and a strip of 2mm foam rubber off an old mouse pad to replace the mirror bumper on the pentax. Its actually an easier fix.
This is the link I followed. http://mattsclassiccameras.com/light_seals/
I remember reading an article where Leica used black wool yarn before using foam rubber. I cannot say from personal experiences, but I have read multiple instances where yarn was used successfully.