The path to getting the G&L fixed is a bad news/good news scenario.
Bad news: We discontinued the two-volume setup for Activators some 16 years ago, and the spares for the volume controls (our part number 475-022) were exhausted about 6 years ago. So to repair, you'll have to change out the two-volume harness for a one-volume harness and pan control (which is a little less expensive than what you paid for your whole Spoiler 18 years ago).
Good news: when you convert, the bass will have less noise in the lower than full volume settings because the filter volume will be proportional to the master volume (instead of full blast all the time like in the current setup). Also, since the system is modular, you'll be able to fix this yourself on your kitchen table. Plus, you're son will also get a new output jack on the one-volume harness.
To order these parts, you can email me your phone number and I'll call you back or you can call us at 707-523-2611 between 11-4 M-F.
Adriaan is correct as usual, the pickups in your Spoiler and your son's G&L are identical.