A head is never acceptable on a new or newer engine, but I've seen issues similar as a new platform is introduced. I still have not seen this as a widespread issue at all. My remark on the 3.8 is from a driveability and maintainable stand point. Having owned the 3.8 I would never be cursed with it again.
'15 Expedition EL, '12 Outback,'07 JK, '06 Mustang GT, '05 PowerWagon,'05 Freestar, '02 Yamaha