/diy/ - Do It Yourself

I have a Mesa/Boogie V-Twin guitar pedal that I want to fix. It works fine when you first plug it in, but after about 10 minutes or so the volume drops so low you can barely hear it. It seems to sound the same though, just significantly lower, so if the gain is set high it's still very distorted as it should be.
The clean channel keeps working as it should.

I found this schematic and marked some stuff on it that may or may not be correct as I don't really know anything about this shit. My current idea is that one of the TL072 op-amps is dead.
Does this seem reasonable or could it be something else?