Repairing a 1978 MXR Envelope Filter Pedal

[cavedude]

This is my first post, so I apologize if this is in the wrong spot! I recently found a MXR Envelope Filter pedal that has been sitting in a box for we estimate at least 25 years. The pots tell me it is from 1978 (making it a year older than myself!)

The issue is, the actual effect doesn't work at all. With a fresh 9volt battery in, I get a clean tone regardless of which way the switch is positioned. There is hardly any difference in sound between the two settings. Perhaps there is an ever so slight drop in volume when I switched to "on", but that is debatable. The only way I can truly tell which position the switch is in is if I take the battery out. Without a battery, the "on" position is barely audible. In bypass, I get a normal clean tone. I assume that means the switch is working properly. I think that also means the input and outpack jacks as well as the battery are working as well. (I do get 9.17v right off the battery according to my multimeter.)

I am a novice in electrical repair, but I do understand the basics. I am using this schematic as reference: https://images.duckduckgo.com/iu/?u=htt ... er.jpg&f=1 (Tough to read, I am sorry!) What I have done so far:

I performed a continuity test on each of the wires. They all seem to be fine.
Tested both pots with a multimeter (they are 500k.) Both work great, and go from 0 to about 480ish.
Mapped out all of the components and tested each of the resistors (that was grueling!) All seem to be fine.
There is a 0.1uF tropical fish capacitor that I refer to as C1 that looked dry rotted, so I replaced it with a modern variant. I have a pair of NOS capacitors ordered so I can replace it with a stock part, but for now I should be able to continue troubleshooting.
Tested both diodes. Both are good.
I cleaned off most of the foam/glue debris, and used some alcohol to clean up some of the corroded points and traces. All have continuity. (When I opened the pedal, the foam basically turned to dust.)

At this point, I am stuck. All that is left are 10 more capacitors and 3 ICs. I don't know how to test ICs, nor do I own a logic probe. I am not sure which to look at next. While I was typing this, I found a very small scratch right above one of the legs on C7 (0.001uf capacitor) I assume that should be replaced, but would that cause my issue? The schematic seems to infer that it is the band pass. I'll be honest when I say I am not exactly sure what that means. Can anybody help out with this? Thanks!