Hey Markus -
That's some great information. I'm looking at installing a Blaupunkt Memphis MP66 4 channel head & most likely an Alpine PDX 4.1. So I'll be going to a 4 channel system all around. And the Alpine will fit in the stock location.
The problem isn't the fader, I've checked that. Corrosion or a connection problem should cause some static, I think, or no sound at all rather than just a barely audible sound. No capacitors, and not likely a blown speaker because it's the entire right side. And through researching on this forum, it seems as though this isn't an uncommon problem with these factory amps.

My goal is just to have a nice sounding system. Playing MP3 is a bonus. I don't want to spend a gazillion dollars on this either.

Thanks Again
John