Rico:
The PT6 series of engines has been around for over 40 years now, and there are tens of thousands of these engines in service on many different types of aircraft.
If you think that the engine is an area of concern in the various accidents and incidents that you have enumerated, I think it would be more appropriate for you to narrow your focus and look at what 'common factors' these incidents have in common. For example, environmental conditions (e.g. hot & high, or salinity), maintenance practices, and even perhaps whether or not the same overhaul facility (not to mention the same regulatory authority providing oversight and control of the maintenance practices) was involved with all of these engines.
I'm not suggesting that this engine is flawless, instead, I am saying that you are taking too wide a view by just 'looking at the engine'. You need to investigate further and determine what other factors (related to engine operations) these accidents and incidents have in common.
Michael