Renesis engines, in general, last about 80-100k miles. Not saying they WON'T last longer than that because there are quite a few owners with 110 and 115k but the general rule of thumb is to take her for a test drive, and run it up to the dealer and have the compression tested and a full diagnostic run on it, which is about $200. Be aware that while these aren't the most expensive cars to BUY, they are quite costly to OWN. Fuel mileage sucks, and parts are expensive ($800+ for a quality cat)...but my insurance company sees it as a sports sedan so it's affordable, and they're ridiculously fun to drive. Something to look in to is buying a GOOD aftermarket warranty for an RX8. Not just something that covers major drivetrain components, like engine and trans, but also expendables like say a Clutch or Coil Packs, as they can get expensive. Also realize that the engine in that car has a 98% probability that it's a REMAN! Mazda ran out of NEW replacements a while before 2009, and thus we get remanufactured engines...which are toss ups as far as reliability. Some last 30k, some last 80k...they're a gamble...hence why we compression test these things pretty regularly, as the inside of the housing is chrome plated, and nobody has found a way to cost effectively rechrome these engines...so when the housings wear out, they're done...finite...expensive paper weight. The car is STILL under warranty, as the car has a 8 year 100k warranty. But it's by the CHASSIS, not the engine. So mazda SHOULD put another engine in it, if it happens to blow before 2017 or 100k (Whichever comes first)
Great cars to own, just gotta know WHAT you're getting in to before diving head first into one of the most unique cars on the planet.