Photo: Ethan Llamas, CC BY-SA 4.0, via Wikimedia Commons
2 faults documented by at least two sources, listed by version then by mileage at onset when known.
2 known faults
The 12 V battery, which powers the electronics and allows the hybrid system to start, discharges if the car is not used for a few weeks. This is the most frequent complaint from RX 450h owners according to WhoCanFixMyCar, and cases of repeatedly draining batteries are described on the Club Lexus and Lexus Owners Club forums. Slow charging is preferable to a jump start.
The 2010-2015 RX 450h uses an electro-hydraulic brake actuator. Its failure is described as common beyond 100,000 miles (about 160,000 km) by Go-Parts: noise, warning light on, code C1391. CarComplaints ranks the failure of the actuator on the 2010 model among the most reported (repair costing around 2,700 dollars), and an owner quotes a replacement at about 2,482 dollars on Club Lexus. Replacement and calibration require Toyota's Techstream tool.
No recurring fault documented for: RX 350.
An OBD scanner plugged in under the steering wheel shows stored fault codes, even with warning lights off: useful during the test drive.
Compare prices of parts for the Lexus RX III (timing, brakes, filters) to estimate the repairs to plan for.