358 is probably a LM358, that's a very common op-amp that has been around a long time.
What I would probably do is trace the circuit back from the affected output and see which IC(s) it passes through, then use an oscilloscope to look at the signal at various points until you find where it changes suddenly, if it's distorted you probably have something like the top or bottom half of the waveform is getting clipped by a bad output. It sounds like you have multiple similar or identical circuits so you should be able to compare similar nodes between the bad one and one of the working ones.
If you don't have an oscilloscope you can use a test amplifier. This can be any small audio amplifier, a set of powered computer speakers, a portable stereo with an aux input or one of the many cheap audio amp modules you can get for a few dollars or less from China. Make a probe out of some wire with a resistor of maybe a few hundred ohms to a few k to protect the amp in case you accidentally probe a power rail or something and then start poking around, you should be able to trace the audio all the way from the output back to the source.