For What It's Worth...

I would look for a bad 20 uf capacitor in the low pass circuit, maybe the one connected to that 10 ohm resistor. The inductor could be bad as well or some combination of the two.

They can be checked with ohm meters to some degree, or you could swap drivers on the two networks and see if the problem "moves" to the other side. If it does, drivers. If it doesn't, investigate the crossover network.

maybe another forum member could repair it for you if it is the crossover network.