So many engine failures on Series I RX-8s (2004-2008) that Mazda extended warranty coverage on the engine core (rotors, housings, bearings, eccentric shaft) to 8 years/100,000 miles in order to prevent an RX-8 owner riot and to re-assure future buyers. The extended engine core warranty also applies to Series II RX-8s (2009-2011) even though Mazda made a number of changes to the engine to improve durability. They added a 3rd oil injector for each rotor, new electric metering oil pumps, increased the oil pressure, revised oil filter, larger oil sump, among many other things. This decreased the failure rate of Series II engines, so now instead of apex seals lasting 60k on average it looks like you can get to 100k without additional "extra" maintenance. Not many Series II RX-8s have rolled over 100k yet.
The common failure mode is carbon buildup on the rotor housings that gradually wears down the apex seals. Carbon can also get behind the seals and unseat them. The problem is that injecting 4-stroke oil is not the best solution for keeping things clean, it was a compromise for the sake of user-friendliness (though some people still bitch about having to add a quart every 1000 miles or so). A better solution would be to inject 2-stroke oil from a separate tank. Hence why the video recommends premixing a little 2-stroke oil into the gas. They also probably compromised on the amount of oil injected for the sake of emissions.
My car was displaying subtle symptoms of low compression (occasional hot start issues and occasional rough idle when hot), but otherwise running well. I wanted to make sure I had good compression before I was out of warranty and before I started doing some mild performance mods. As compression deteriorates, symptoms would have gotten worse, progressing to stalling at idle, real difficulty hot starting, misfires, loss of power, flooding. A reman engine from Mazda is about $5k out of pocket these days, and I believe a custom rebuild from a shop can run north of $6k.
2009 Mazda RX-8 R3