Dont replace parts just on suspicion. Unreflected activism may lead to more trouble than intended to resolve.
Think thrice before igniting the blowtorch and touching the system.
I urge you to get comfortable with an Oscilloscope and to try to understand the schematics which BTW are good to read. Use colors to mark signal flows, CV and audio.
If there is a problem with a whole group of parallel circuits ie.the voices, the problem most likely is located upstream thereof.