Stereo Troubleshooting

I'm looking for someone with experience with troubleshooting stereo amps, or other electronics.  (Greg, I'm looking in your direction.)  Basically, what's happening with mine is that the right speaker keeps dropping out.  If the fuse in the back of the amp is removed and then re-inserted, then the speaker will come back, only to drop out again several minutes later.

The amp itself is too old to bother taking to a repair shop (as repairs would likely cost more than it's worth).  I know it's not the fuse itself, as swapping the fuses for the left and right speakers has no change on which speaker drops out.  Further more, the channel itself never completely disappears, as you can always faintly hear some of the higher frequencies coming through.

Anyone?

Edit: And it hasn't messed up for the last hour or so.  Maybe it will stay like this.