Looking at the most recent ATSB stats report (AR-2013-084), we can get a guestimate of the engine failure rate for GA by adding the accident, serious incident and incident counts for "powerplant/propulsion", and diving by the total hours. For 2012, we get a GA engine failure rate of 0.16 failures per thousand hours. Note that this includes single and multi engined aircraft, and both piston and turbine, so it's not exactly comparable to the jab/rotax numbers given by raa. Also, there's probably differences in counting engine failures vs prop failures.
There are RAA numbers in the same stats report, but those numbers look seriously suspicious.
While on the ATSB website, there's an open investigation by them into "light sport" engines (AR-2013-107). It was due to be released last month, but that has yet to happen. Perhaps that report has triggered CASA's action.
- S