Hi Krusty (and a happy New Year to all)
My understanding regarding JAL 123 is that the repair job done by Boeing was indeed not up to scratch however as part of the deal Boeing required ongoing periodic inspections to be carried out by JAL; for whatever reasons they were not carried out or else (hopefully) the faulty repairs would have been identified and tragedy averted.
For this reason one of the senior JAL engineering managers topped himself thereby "accepting blame" on behalf of JAL and of course in the Japanese psyche any problem or negligence that might have existed, ceased with this action.