Be very very careful if you disassemble the unit. The capacitor is "charges" at 300-500v and can deliver a significant shock even when only partially charged. Simply removing the batteries will not make it safe.
Given the symptoms, my guess is a bad flash tube:
- recycles enough to light the ready light = recycle circuits function
- recycles enough to light the ready light = capacitor is at least holding an adequate charge
- delivers a spark across the sync terminals = sync cord is OK
There might be something else faulty in the trigger circuit, but these antique beasts were rather simple designs. They did nothing to protect the shutter contacts or the photographer by isolating the high voltage.