I think suspecting the electrolytics is a good bet. Recently I've been overhauling a Personal LaserWriter LS power supply containing 1992 date code original parts. Of the first five electrolytics that I have examined then replaced, ALL FIVE were leaking liquid electrolyte (I checked that it was not flux residue). The power supply would not start up but changing these resolved the startup problem. I'm talking about conventional radial lead electrolytics, not those pesky surface mount parts that we already know are troublesome when old.
The leaks were appreciable. I found them by reaching in and wiping the noses of the caps with a clean bent piece of bare wire then inspecting the wire for picked up sticky liquid. These particular caps were spaced above the board so it was easy to probe their lead seal areas.
Electrolytics have long been a necessary evil in electronics. I'm seeing evidence that 1992 electrolytics of conventional construction may be reaching end of life. I'm going to replace all of the remaining ones in the supply that I am overhauling. The larger ones may have much more electrolyte to spare, but they also have to withstand very high ripple current heating from the motor drives in my printer. I also do not like what electrolyte can do to PC boards if left there long enough. [
!] !]'>Edited post: Important switching power supply safety note: The physically largest volume capacitor usually is the one that is charged from a bridge rectifier connected to the power line voltage, and stores a potentially lethal amount of charge even after the line is disconnected. There's usually a bleeder resistor path to discharge it over a minute or so, but designs vary and bleeders can fail. The catch 22 is that the topside of the PC board offers few clues as to test points to measure and if necessary discharge this capacitor before unmounting the PC board. So any probing for leaks, and unmounting the PC board from the enclosure, must be done with caution and appropriate insulation. Keep in mind that any of the caps may have some remaining charge.