I have seen the original knobs on the OP-1 show defects and cracks. So I have developed a kit of knobs that is as reliable as possible to the original and I have reproduced it by means of 3D printing. I’ve done a bit of R&D work and have finally managed to develop ones of acceptable quality.
If any of you are interested, he can find them at a reasonable price on Etsy via the link below
I leave here some samples so you can see the pieces.