This was probably routed before most of the CAD tools were in good shape. It looks like there is a lot of cleanup that could be done now. Even this little section is a mess:
It's a relatively simple design and just moving a few traces around clears up space for further cleanup and refinement...
Schematics would help, but a problem that fixes itself as you described sounds like a bad cap. Is this the board in question:
I think that board generates the different voltages used by the machine from the main battery and/or the power brick. If you carefully probe the caps on this board...
Do you have a power adapter for a PowerBook?
forums.macrumors.com/threads/how-to-use-a-g3-g4-power-adapter-on-a-clamshell-ibook-pismo-wallstreet-lombard-pdq-powerbook-g3-1400-3400.2393395/