Engine is dead..
 

I just own my 8 for half year and towed two times for repair.
Is 2004 RX-8 have such many problems?

In Dec 2007, I just drive carelessly through a flooded area. Intake gets wet and spark plugs get wet. Mazda dealer needs me to pay $1500 for the spark plugs,engine mount Gosh!
In the end of Jan 2008, my car was died in a sudden.
Two weeks later, Mazda dealer told me that my car engine was dead.
And it needs $12000 in total to replace a new engine.
By now I am putting my 8 in Kansai performance shop and waiting for the engine replacement. It still cost me $6000 to fix it.

A technician from Mazda dealer told me that after RX-8 went up to 80000 miles there will be some problems on the engine(just for 2004 model)
Is that true?

all 04 models had a recalls on the engine you should have gotten an 06 and up model

I don't think you can blame mazda for your driving through water deep enough to drown your engine. I also don't think you can blame mazda for anything that went wrong with the engine after you drowned it. I've had ZERO issues with my 2004, and I've had her since 03.

Talk to Paul at Mazmart. They can get you a rebuild for ~$2K.