Not sure that the PT6 and sulfidation of the blades is an issue here...there are several companies, most notably Harbour Air and West Coast Air, based in the harbour in CYVR that use DHC-3t and DHC-6 products on a daily basis, and have done so for many (20+) years. The engines go through a compressor wash every day. I'm sure if they had a problem with turbine wheels letting go, then Transport Canada wouldn't be letting them fly single-engined (DHC-3t) over what amounts to open water...nor would the companies expose themselves to that kind of liability. 'Course, Chalk's might not wash evey day?