Since the radio is playing and you get a hum most likely the filter capacitor replacement as mentioned would solve the problem(s). You would not need a schematic to replace them and probably cost would be inexpensive. You can tack in replacements since they are not shorted to determine if indeed they are the problem.
However if he is looking to upgrade to bluetooth it would be necessary to send it out to a dealer such as myself to have the boards installed as they are not sold. Appearance and fit remain unchanged for the conversion.
You can look this over from Aurora Design: http://tech-retro.com/Aurora_Design/FMR.html; http://tech-retro.com/Aurora_Design/BT.html
to get an idea what's available.
Please feel free to contact me for additional information.