Run 300C models for about 15 years at about 300 to 500 hours a year.
The only unscheduled maintenance in the past 3 years / 1300 hours has been
1. cracked skid - while wheeling it out ( last week ) $ 2500
2. Clutch actuator failed $ 500
3. radio display u/s £ 120
If I go back another 3 years and 950 hours
1. Engine overspeed - student started with throttle fully open £ 11000 but insurance paid
2. Broken ring gear £ 470
3. Trim diode £ 25
4. Trim pivot pin sheared £50
I have owned 7 different machines all generally not a problem if you
a) Keep it in a hangar
b) warm it up and shut it down properly
c) LOOK AFTER IT
d) Use an engineer who knows the type
Their biggest problem is they are not user friendly eg changing the oil filter needs belly panel off, although new ones you don't need to do this. Blades - erosion strips will only last 3 years unless looked after really well. Just bought a new set of blades and strips sealed up much better.
If you have the old cone feathering bearing change to elastomeric fork will save a fortune.
Now one of my customers left his outside with no covers on for 6 months - £ 10K later it is up and flying !