I bought a replacement volume wheel for the GBA. There are no other potentiometers available for the GBA. The original one has 30 kΩ as shown on the schematics. The one I bought has 10 kΩ and can be bridged to 5 kΩ. The name is "B103". It was sold as GBA replacement volume wheel.
Can I use it?
I asked a different question about the GBA hardware on SE electronics and they told me to ask here. So I hope this is the right site.
Edit: It was told to bridge PINs 3 and 4 (from left to right on the photo). Then you have 10k fixed and 5k variable resistors. It worked well. But I don't know if this is the best solution.