Have you checked the fuses and fuse holders on the solid state flipper driver pcb in the cabinet?
Often the fuse holders go bad causing this problem.
Also when you measure only 6,5vdc this means you’re either measuring wrong or there’s a bad contact or leakage somewhere. My bet would be the fuseholders not clamping anymore onto the fuse.
Compare with other high voltage coils, i think you should measure around 50-70v if memory serves me correct.