No help, unfortunately.. only questions..:
Pictures of the failure site ? have all the failures of the disks been the same?
120 HP is a lot compared to "normal" stuff.. I wonder if they are using the correct disk for your engine/trans and not using a "Will Fit" disk. If the disk is not rated for that power, the springs would run fully collapsed and the disk would be subject to a lot more fatigue.
Quite unusual to have that many fail in those number hours.
Has someone measured "runout" of the flywheel disk mounting surface and the runout of the trans input shaft? A bad mount or a little dirt between the flywheel and the crankshaft could cause enough runout wobble to fail a disk pretty quickly. Same with a slightly bent transmission input shaft.
EDIT: Beautiful boat ! and Welcome Aboard, Sharon.
