It's not the focusing ring that is missing, but the focusing tab. But if it is like the YK, you still would need to tear down the lens to replace it, as it screws on from inside the focus ring.
I don't know if you really need a blow dryer to soften up that old grease, I would try putting the camera beneath a desk lamp, that may warm it up enough to get it turning, and maybe a drop or two of naphtha will suit to re-amalgamate that old grease. But it probably should be torn down and re-greased.
The lens assembly on the YL might be similar enough to that on the YK or J that some parts may be interchangeable (it looks the same in pictures, at least), so that gives a little hope as to availability of parts.
Considering the rarity of the camera and it's obvious sentimental value, I'm with Phil; it is well worth getting that fine old rangefinder serviced professionally. If I were you, I would get in touch with Mark Hama (http://www.markhama.com/
) or Russ at Camerarefurb (http://camerarefurb.com/
), both of whom specialize in reapair of Yashica rangefinder cameras.