Modern caps are built much better n leak alot less due to metal casings n special directional expansion slots to keep em from exploding like bombs n catch fire as they once did.
I had an old studio 4 head Balcor that used 16 huge caps the size of dry cells. When that thing finally went the tops of a few caps blew n sounded like a welder with a stuck rod for a couple of seconds, that high voltage hummmmmm, then POP!.. lights out in the building. The stech of electronic smoke like a florecent balast cooking n the main entrance circuit breaker checked out. When I opened the box to see what the problem was several months later, I followed standard proceedure handeling caps, discharging the remaining uncooked ones, I noticed they were still fiully charged. Balcor diagrams showed a slow bleed circuit but it must be a very slow bleed. So don't think your caps are fully discharged because it has been sitting around for a long time, they do take time to bleed off.
I fired up an old potato masher Sunpack 611 after not using it for 35 years. It whistled as it normally does then settled in to the usual beep beep beep so, out of habbit, I fired it at full power a few times. No problem at all n I have been using it regularly for the past year, even made a battery replacement using a sealed lead acid 6V battery.