Been a long time. Now I have many hours of soldering experience. Conquered two practice boards, recapped 4 Game Gears successfully among other repairs to fully restore them and even built a fully custom one, and built a custom GBA with upgrades too.
Opened up the Duo-R, reflowed all the pins for the A/V connector. Absolute piece of cake. Not having any issues. I played Valis III like 2 hours and not a single issue loading audio. No sign of capacitor issues anywhere -- even the repairman said Duo-R's are much better and typically don't have an expectation of requiring a recap because the hardware is better. Nevertheless I could easily recap this thing myself; after doing multiple GGs honestly I think I can recap anything. Mega CD regular Duo's etc.
So my tip to anyone having minor A/V issues, wiggle your A/V cable behind the console and see if it causes any interruption to the signal. If it does, reflow the pins for the connector. Cold joints are responsible. If you can handle a soldering iron at all, you are equipped to perform the task.