[KCMike]

No, ain't no expert in that.

But before going inside, I would try to (even though I think they are OK) bypass all circuits between MPX unit and control amp by disconnecting everything first from MPX's L/R outputs, and from Con amp IN1 and IN2 inputs and then connecting them respectively L to IN1 and R to IN2.
If it is still low vol, then further exploration into FM circuitry is warranted.

I tried what you suggested. But want to be clear on if I did it correctly.
Unhooked the L & R wires from MPX output pins. Unhooked Con. amp IN 1 & IN 2 wires.
Used jumper wires and connected one to each wire that I had removed from MPX board L/R .Then hooked the other end of each jump wires to each pin( -L to IN 1) & (R to IN2) of Con. amp. I powered up this way on variac and all I got was a hum from the speakers.
I don't know if this is helpful but touching/scratching/tapping, the chassis or the switches with no knobs causes a scraping and or tap sound out of speakers.