The typical overhaul period for a PT6 is 3500 hours of operation. You must inpect the hot section of the engine for damage at half life, of 1750 hours. This means disassembly of the engine to get access to turbines, nozzle vane rings and the combustion chamber.
The highly loaded gears in the RGB can start to wear excessively and produce metal fillings. Evidence of this would be detected on the magnetic chip detector and/or in the RGB finger screen. If this happens, it must be removed and sent for overhaul.
1: Engine Construction & Operation