Operated PT6 powered aircraft when they first became available in the USA (1966...DHC6 and BE99) and found the engines to be very rugged and reliable.
The commuter airline that I flew for at the time had 32 twin otters and 15 BE99's, with a large variation of pilots, older military guys and younger civvy guys.
The FAA allowed on-condition maintenance after about three years of operation, with hot section inspections at each 1800 hours, as I recall. Overhaul was at 4400 hours.
Some of the older military guys paid no attention to the torque meter, preferring to set power by ITT and RPM (it worked on the B47, so should also work on the PT6). This practice is most definately frowned upon by Pratt&Whitney, and leads eventually to power turbine/gearbox failures.
The only engine failure that I recall was just after takeoff at 200agl, the prop governor pilot shaft sheared, and the prop feathered automatically (no oil pressure to prop, feather results).
Hope this has been of assistance.