Heat comes from energy. Its about how much power the engine produces and how effective the cooling, not the fuel that supplies the energy. I have only half been following this thread, but I think some of the failures may not fit the symptoms. I struggle to see how fuel type would play a role. Ignition timing might (come in Jaba).
As a rule of thumb car sump oil runs about 20 degC hotter than the water temp. Modern cars can easily run over 100 degC, so an acceptable operating temperature for oil is 120 degC (say 250 degF) for as long as you like. Use Synthetic and you'll go a lot higher. Higher temperature causes mineral oil molecular chains to break down. A modern car will happily do this on a synthetic blend oil for 30,000 km which equates to about 150 hours (an overall average of 50 km/h is a reasonable guess for an average suburban based driver with a mix of city, suburban and freeway driving). The Jabiru (I believe) uses automotive oil not the old mineral cr*p that certified engines use.
Oil is a major part of the cooling of any engine (even water cooled ones). I forget the proportion of cooling done by oil, but it might be circa 20%. Automotive oil will have better " wetting" properties and I would expect would transfer heat more effectively that aviation oils.
We should be able to design & build engines to cope with this and I struggle to see how through bolt issues are related to operating temperature. If I were to investigate this, I'd start by looking at the operating practices.
As I said, I haven't really paid full attention. These are off the cuff ideas. I might have something wrong.