My 1986 BMW's 528e RADIO stopped working: first light then I believe the fuse.
Is it better to repair the radio or but a rebuilt one.

You may be able to get a replacement from a junk yard for $5 or $10.
(you pull it apart and save)  My guess is rebuilt is about $99 or
almost that much to get it repaired. I would try a new fuse before I
did anything else as there is an even chance it will fix the problem.
The speaker plug might be disconnected from 18 years of vibration. The
pilot light likely needs a new bulb, but you can likely live without a
pilot light.  Neil