Well, now you know. At this point, if you want to salvage the board, you have to escalate to the next step and recap the board. Of course the possibility exists that a leaky cap destroyed something on the logic board, so if re-capping still does not solve the problem, the next step is a thorough investigation of the board under a magnifying glass. Since the caps are the most likely culprit, and will need to be done eventually anyway, that's your next step.

Go ahead and wash the board with the sound problem as well. That may fix the problem even though it did not on the video problem board, but it will eliminate possibilities. The sound circuitry is a little more localized, so you might be looking at a much smaller fix. Of course it too could have board damage, but again, much easier to isolate.

Hopefully some of the SE/30 folks with the experience with this will weigh in and offer more help at this stage.