What you describe is "normal" for the failing capacitor syndrome. It starts as an intermittent problem and gets progressively worse.
I see.
The problem is with electrolytic capacitors, which are little cylinders filled with a solution:
http://en.wikipedia.org/wiki/Electrolytic_capacitorThere was a rash of problems with these more than a decade ago:
http://en.wikipedia.org/wiki/Capacitor_plagueThe nature of the function of capacitors means failure typically doesn't result in a complete system failure, but little issues. I think it might be D-lite's mod page that says your system needs to be able to run well for two hours before you ship it to him (things change as it heats up).
For what it's worth, a capacitor actually burst on my Duo, putting brown fluid all over the main board. Even so, it still turns on, games play, and there's sound. However, the chance for failure and various other problems means fixing it is probably a good idea.
For my part, I'm probably going to ship Duo to Nat to be fixed some time soon when I have time to pack it up and such.