It's almost two years to the day since I got back my '78 6.9 from the repair shop where I had all five spheres replaced. This afternoon while driving home from work, the bounce has returned signaling the demise of one or more of those spheres. Bouncy bouncy is how I would best describe the ride home. Taking a poll of the reading audience: How long have you been able to run before having to replace these spheres? And what diagnostic steps should my repair guy take to diagnose which one or ones have gone bad? The last time this happened, it cost me over $2K in parts and labor to replace them. Not happy.