Derek,
Thanks for the pics, that's a sweet looking bass! (For future reference, you should be able to attach more than one pic to a single post, but this worked fine too).
So the pot that spins all the way around is the one closest the bridge on the front, the small square piece in the last of your photos, right. In case you didn't know, reply #9 above is from Mica Wickersham the youngest of the family who own and operate Alembic. Whatever she says is the truth!
My suggestion would be to order a replacement pot from Alembic so you can get the exact component you need. Then either install it yourself or get some help with the soldering and shrink wrap. Since that pot is on its own and not soldered to a circuit board the task is not that difficult.
Both set screws need to be loosened in order to pull the knob off and determine the size of the shaft they're mounted to. Do that before ordering so you know if it's the 1/4" or 1/8" shaft version. Try calling Alembic late-morning to early afternoon CA time. Mary is usually the one who answers the phone.
Keep us in the loop!
Jimmy J
