I can’t see much from the photo but if the encoder shaft is broken, the MD will need to be disassembled and the encoder desoldered and replaced. If you are not capable of this yourself, I am guessing this will be at least $100 from a regular tech and (probably) quite a bit more from Elektron. The other encoder may be dirty or it may need to be resoldered or even replaced.
Not a known issue for the rotary dial. As Veets said it is likely just dirty. You can work without it in most cases if for some reason it is a deeper issue.
For the broken encoder. I have taken my MD apart and it is pretty easy to disassemble. If you can solder and you have a new encoder to replace it with then this shouldn’t be that hard to fix. The board is only being held down with a few screws. I do remember a ribbon cable in there somewhere so just handle it with care and be sure you are grounded when handling the PCB’s. You don’t want to add more problems to it. If you are unfamiliar with soldering then it should still be a piece of cake for anyone with experience.
I’ve had the rotary dial jump values since I’ve owned my Machinedrum. I’ve never worried about it too much, however I’m wondering if there is a way to clean it without having to take the whole machine apart. Maybe a good cleaning will help to fix the issue. Thanks!