No good talking to Steve Swift ... he'll just send you to me. I'd be more worried about the J2BDs .. $100K aside. The AD is based on data supplied by Piper as the manufacturer. There is no difference between Boeings and Pipers. CASA writes the requirements and Piper gives the data. It was a corporate aircraft. Piper did a simple test and came up with 13,000 hours for the -350 - it should have been better but Piper did not want to revise it. That is the way it is unless you can get some underpaid bunny to recrank the calculations. That was not going to happen until the pilots strike in 1989. Even then (28 years ago) there were timeX PA31s pushed up against fences. Rather than do a fatigue test again, it was taken across to safety by inspection and all those timeX were back in service. There were a lot of happy faces, particularly at Hazo's who had twenty odd. The FAA have found cracks in a Chieftain spar cap (not good). I suspect it was a "Friday arvo" aircraft ... I found a couple. They do have corrosion problems. ... And I'd learn a lot about detonation ... 100LL can't last forever.