NicJimBass
Flossin'? I thought your name was Munson!
You might look into a simple resistor or cap swap or addition to tame the preamp. I have a '83 G&L El Toro and they are known for being rather bright sounding basses, much like the Stingrays and active Fenders of the same era. I was on the Basses By Leo/G&L bass forum and the man who designed the preamps for G&L is a regular poster and fountain of info there. He told me of a simple mod by placing an additional resistor in series with the hot signal wire right at the input of the preamp to tame the brightness. I played with resistor values and landed on one that mimics the treble content of the bass in passive mode. It didn't have any effect on other frequencies except the treble. Cheap, simple and effective.
Another mod is adding a loading cap across the hot and ground of the pickup(s). These lower the resonant frequency and can quickly and cheaply revoice a pickup to be less bright.
I'm actually having the opposite problem this time around. I have to really boost the treble control to get some decent brightness out of it. The preamp seems to be more subtle than I remember it being.