The bolted joint at the flex plate failure location was found to have a single thin washer under the bolt head and nut, and no spacer washer between the yoke and flex plate. This spacer and washer combination was different from that specified by the manufacturer for use with a NAS6605-6 bolt.
From the ATSB report - see here for more
http://www.atsb.gov.au/media/2786447/aair200401917.pdf
I stand corrected, the pal nut was fitted
Further reading says the pal nut MAY have not been fitted