Jeff Urban wrote:

I have seen some strange ground fault problems. Try to think back, if
the drives were not mounted, were they in electrical contact with the
case ?


One of the drives was in my hand when it burned out. That
is the one whose C651 melted. In the other two instances, the
metal of the drive was in contact with the metal of the case.

I share your worry when a problem just seems to go away.