I bought a used OT about 2 month ago. It was one of the earlier models with the rough metal.
The encoders were somewhat loose and not as precise as I would have liked them to be. So I ordered some new encoders from the Net. I got the part number from this post on Reddit: https://www.reddit.com/r/synthesizers/comments/6fc0bj/repairing_my_octatrack_encoder/
They are the “Bourns PEC16-4020F-S0024”.
Maybe it was a mistake by the supplier, but the ones I received are indented. (They click into place on every step)
I am still waiting for the company to get back to me, in case they sent me the wrong ones. They look identical otherwise, and they work perfectly. They feel very solid and when I now go to grab an encoder, there is no wiggle anymore. The behavior of the encoders is surprisingly fun, as every click is equivalent to one value on the OT. The precision is now fully there.
If you have any question regarding installation / feel, just ask.
Thus I believe I currently have one of the only OTs with indented encoders.
EDIT: See this comment on reddit: https://www.reddit.com/r/synthesizers/comments/6fc0bj/repairing_my_octatrack_encoder/dnl6r9b/
I had ordered the part number PEC16-4220F-S0024 not the …4020F…