I just came across a thread asking about "the RX8 with the most miles". (or some such wording)
I'm happy to hear there are a few with big numbers..
I think it would be great if a few of the owners with more then 100K
( still running and no engine rebuild) tell us their secret to keeping it going.
I would guess that most new owners would like know..
Maybe this is covered before but no luck in doing a search..

 

I had 160k miles on my first 8 when it was totaled (rear end collision). I drove it hard regularly. I made a round trip to North Carolina (DGRR) from California with 130k on the original motor with no concern.

Change the oil every 3k, make sure you use the right filter. (don't over think this, just do it.)
Flush and replace the coolant every 2 to 3 years.
Don't let the car overheat.
Check the oil level every few fill ups. carry a bottle of oil so you can top off when needed.
If something doesn't feel or sound right, investigate and make repairs as needed.

The manual covers scheduled maintenance and will get any new owner pointed in the right direction.

There is no magic bullet, stay on top of your preventive maintenance and drive the car.

 

Some people live to 105, others die at 30. You can avoid common problems by reading rx8help.com or the New and Potential Owners thread on this forum, but there's no magic formula for long life. Considering the youngest 8 is now 12 years old, any one you get comes with previous owner problems (big or small). So I think all of that is the wrong thing to worry about, if the engine dies, plan to replace it with a known good one built by a professional and it should last you another long while. It's generally more enjoyable to run a fresh engine than to nurse along a borderline one for years.