I've seen those 'Boomer' amps on the RS4 and RS5 boards, also on some of the ERR and Legacy sound boards. Without a block diagram, I couldn't say what the 358 op amp is for. I like to gawk at the boards once in a while and look up the components to get a rough idea on what does what. I still can't get over how overbuilt the old RS4/5 power supplies were. I can only guess that their audio engineers wanted zero sag when driving the sound. Whatever they did back they did well because those are still my favorite sounds.
I got one of those ESR meters for testing caps. I'm becoming a fan of all the cheap ebay/Amazon test equipment. You have to outsmart them a bit, but they are kind of fun to play with.