Put some masking tape around the end of the spool and place that end on the silver gear (left side) in the take up area. Now this will work fine without the bouncing from a grooved spool. No need for backing paper or such for testing.
The D mechanism is pretty simple. If exercise won't loosen it up, the hardest part is going to be getting the leatherette off. And remember, the leatherette is not for light-proofing, so using the camera without it is fine (Grip-Tac from cameraleather.com is a great material for TLRs).
Yashikor or Yashinon, I only asked in case you were going to sell it Yashikor is a very nice lens, the D is a great TLR- simple but solid nd nice quality. I hope you get it working and have some fun with it.