I'm curious if any others have reached > 300K miles and > 15 years without any hybrid system issues?
Our 2006 RX400h finally died this past December, after ~17 good years, ~280K miles, 2 front deer hits, and one accidental diesel gas fill .
We are pretty sure the hybrid system finally gave out on one of our kids, on a highway in Baltimore, but coasted to a safe place for a tow.
We decided this was the end for "Sylvia", since too many Christmas lights flashing, including the "Check hybrid system".
If by chance anyone is interested in replacing their 2004-09 RX-based OEM stereo with a double-din system, let me know, since I kept the newer replacement unit during our trade-in.

 

You might have nothing more than the hybrid coolant pump failure. When it fails the hybrid system will throw a lot of codes. the pump is about $240 and is mounted on the frame infront of the front left tire. We have 277k miles and the pump has been replaced once.

 

My 2008 Lexus rx400h is still going strong with original hybrid battery, engine and transmission. Last year I replaced shocks and control arms. The vehicle has now 349,000 miles and recently started overheating the engine. My best guess is need to replace a water pump along with timing belt and tensioner. This vehicle is very reliable and I hope to stay alive till I hit 500k miles and it will be a record breaking.