I've found gas generator turbines damaged that could have flown as much as 500 hours with no compliants or noticeable power loss. The damage was caused by the air union at the 12:00 postion, the internal part of the union had broken off and gone through the turbine. I've also seen the engine wash valve sold by Aeronautical Accessories fall apart and cause damage. Arriel engines do get FOD fairly easy, but dust and grit should only give you some light compressor wear and/or FOD.