BTW - I had a GX9 about 3 years ago with a F-50 in it. That engine didn’t have a TBO (Time Between Overhaul). It had a TBS (Time Between Seizures) of about 10 hours.
I finally threw that engine in the scrap heap and put a Stihl chainsaw in it. But that wasn’t ideal either because the crown gear gave out and can’t get any parts for a Gaui helicopter.
I was just about ready to give up on piston power and experimented with electrics. Electrics are toys and they didn’t work either.
Then came up with a conversion for a Zenoah engine, never looked back. Got over 500 hours on the first one those I built.