Lonewolf50 - apparently the cause was an incorrectly torqued anti-flail mount on the TR drive shaft that came loose, slid down to the next TR bearing mount and jammed against it then gradually sliced its way through the TR driveshaft itself.
Thanks.
Hadn't realized how robust the spec was on Apache.
even in an Apache with undercarriage and stroking seats designed to absorb over 25 G of vertical impact.