I recommend you conduct your own research for "Known faults on 2007 Lexus RX350" or similar. I researched before I purchased my RX350 Sports Luxury three years ago from Lexus of Perth (Dealer Principal's vehicle) and do not recall a "known fault" relating to the torque converter. Those I did locate were:
Water pump starts to leak 50,000 – 70,000Kms.
Low rate of idle run (readily solved by cleaning the throttle body once every 50,000Kms).
Engine noise at start-up is typical of 2GR engines & associated with VVTi system.
Idler Pulley Noise due to defective No. 2 idler pulley. May exhibit a squeaking noise while engine is running, refer Technical Service Bulletin T-SB-0056-09 for
2GR-FE engines. No. 2 idler pulleys can be accessed through the passenger side wheel well opening.