Having recently got back into playing with these things, I can say that if your 68k Mac is one that has surface mount electrolytic capacitors (the little silver cans) they *are* bad and replacing them all is the *only* thing that will reliably fix the machine. There's no point in even chasing down all the random symptoms they cause, just replace them all, wash the board off and go from there. Every LC pizzabox I've been in lately has bad caps in the power supply too, haven't come across a 68K Mac yet that replacing the capacitors didn't fix 100%.
The problem is two fold, first, they leak corrosive, conductive fluid out onto surrounding components and second, once the fluid leaks, the capacitors can no longer do their job. Replace with tantalum or ceramic chip capacitors and you will never have to deal with them again.