If you let the flash charge and run for a while without flashing it, the capacitor might re-form and the flash begin to function normally.

Sometimes the capacitors will come back to life, more often they don't. But it's worth a try. I have an old Honeywell from the early 60s, if I let it sit without use, the capacitor loses it's form. Charge the capacitor for a while, and the flash functions normally; I use it as a slave.