I think that RA-Aus has some culture issues around this sort of thing Viper. From what I can understand and have read, the early days of ultralights was plagued with engine failures, and I believe that might be a member or two here who have had in excess of 20 or more engine failures during their time. Certainly if you read some of the US forums where they fly unlicensed, unregistered ultralights, things like engine failures are still quite commonplace.
So the culture is to shrugg off these sorts of things. CASA doesn't want to really know about it, the ATSB hasn't the resources or interest in investigating, and RA-Aus probably neither the technical knowledge (although some specific people may have), funds (investigations can cost a lot of money) or perhaps even interest (already alluded to). The a/c owner is facing a loss of income until the insurance comes through and a suitable replacement can be found, probably an insurance excess and quite likely a rise in insurance premiums in the near future. And they probably aren't hugely keen to spend money trying to track down "why", when there is no return for that money spent. I feel your pain, but it seems that real investigations or outcomes from recreational aviation incidents are little more than a pipedream at the moment.