did you find the answer?
here’s the service manual (I’m troubleshooting a broken em-1 myself), check there:
http://www.warningwillrobinson.com.au/manuals/Korg%20EM-1%20Service%20Manual.pdf
Looks like a fairly standard 9mm upright PCB mounted pot. The D-shaft axle seems to be 25/15 overall/d-shape in length. Also, it has a bushing. My best bet is that it’s a Panasonic pot. The value has to be in the service manual.
Doh! I should have clicked the picture instead of just blazing along. It’s definately an Alps. I guess the extra legs means it has a switch. Then it will be harder to find… The remedy here is probably to get in touch with Korg service.
There were a couple of metal shaft pots with bushings that had longer shafts, the issue then is if the bushing fits in the panel hole, or if you have to drill a bigger one…
It’s still an Alps. Just the variant without a bushing. The similar (compatible replacements) Panasonic EVU-F don’t come in any switched variants at Mouser as far as I could see.
I’m sorry, I was away for some time. It’s good for me, I found the component near my house in order. Thank you for your research.
Now I have the full service manual, it’s great.