My radio works, though it's intermittently died a few times over the past year, only to come back after a night of resting. I have found water in the battery compartment(I've since cleaned the drainage holes) and assumed it was probably water damage.
In fact, the car actually has an e46 amp next to the battery. So I guess the previous one was also taken out by water.
Has anyone tried this guide?
https://www.bmwgm5.com/K-Bus_Troubleshooting.htm