I never used my RC cars that much (I imagine that we've gone through between 16-20 gallons of fuel), but FWIW, my brother and I have had 6 HPI engines in the past 12 years.

The most severe problem I've seen is a one-way bearing that slips on my brother's Savage SS. Take it apart and clean it, and it's fine.

I broke the pullstart cord this winter on my Savage SS (which may have been from rubbing against a body). I've never worn out an engine. That engine will be seven years old this May.

 

my dad flies both Helicopters and Airplanes and has engines from when he was a kid that still run good.

 

After not being used for a couple of years, my five year old 18SS engine started very easily.

I also finally mounted the body that came in the kit. I needs to be lowered and trimmed a little.