AVGAS in the PT6..
I have used AVGAS in a PT6-34 many years ago, from memory the limitation was no more than 100 hours use during the overhaul cycle (3,500 hrs.) from the pilots perspective it was OPS Normal... If you care to Google VH-AAV Sydney February 1980, you will come across the ATSB report on this accident, some thought that fuel contamination due to micro-biological growth might have been one of the factors.