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.
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.
Craft stores sell a material that works very well. Cost just a couple of dollars for a 9x12 sheet. You want the type with the self-adhesive backing.
I worry that your black-yarn-light-seal-technique might bring fibers into your camera. Food for thought. Yarn and camera don't seem compatible...but I might be over thinking this...
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.