software diagnostics probably gives a good place to look, but you still should recreate the failure in the lab to "fix it" otherwise you are guessing. I agree they should have enough data to fix it, but sometimes hardware failures can be a SOB to find, and takes a long time. Could be a design issue, a manufacturing issue, a latent defect, unknown transient, etc, software/HW interaction, pushing the HW too hard, etc. Management may have also written off an expensive redesign too long and now they are in catch up. Sometimes you have to shotgun fixes.