The best thing you can do for your 30+ yr old retro computer is to recap it. The electrolytic capacitors just loose their juice (actual fluid) over time. Keep in mind, it doesn't matter if the voltage rating on the capacitor is higher than the original rating.
The Rev 4 motherboard needs 29 capacitors
The Rev 6 motherboard needs 32 capacitors
The motherboard is plenty safe to do yourself. Keep in mind the capacitors by the Zorro slots can be either radial (can sitting on top) or axial (lying on its side like a log).
Check out this link for some power supply recapping information. Remember, those big caps have enough stored electricity to give a serious shock or kill you. Follow proper safety procedures for discharging them before you go poking fingers or metal objects in there. See — http://blog.worldofjani.com/?p=6375