I bet I know what doolico does for a living...

Regardless of how the engine is mounted it will be pulling against the mounting lugs. That's unavoidable whether it's mounted on an angle or directly in line with the airframe. The mounting base of the case is a solid structure, not tabbed as with some other engines so the addition of a flat mounting plate between the mounting lugs and the standoffs would add little, if any, additional torsional support. The only thing that I see wrong with the mounting is a lack of flat washers under the mounting bolts, placing two dissimilar metals against each other and permitting a harder metal to vibrate on a softer metal over a small area.

I would send the engine to an independant specialist, one that knows 3W engines, to inspect the engine for another cause. I have a pretty strong feeling that an internal cause will become evident on tear down by one that knows what to look for.

Cases breaking is not something new for 3W, in fact it's was something that happened fairly often a few years ago. As with anything else, if you write enough restrictions and warnings in a manual eventually you won't have to warranty any product because the conditions of use cannot be fully complied with.