Re: Who's at fault? - You make the call $250.00 each
From the School of Hard Knox Lesson # 9,857.31215:
"When in doubt, blame the other guy and see if you can get away with it."
If that does not work, admit joint and severable culpability and pay your dues to the School of Hard Knox. $250 Each.
Yah yah, life on the streets is tough.
Since the equipment was in late stages of deterioration, and the driver's use of the vehicle made it worse both may be liable, unless the lease and the master lease say, imply or suggest otherwise.
(Disclaimer since I am no Solomon nor Clarence Darrow or Don Nathan, my remarks may be completely ignored in whole or in part.)
If the catalytic converter is rusted out, and it's required to be in good working order in order for the vehicle to be leased out, then the owner of the vehicle is responsible for fixing it.
The fact that it took an incident of some type to uncover the state of the converter does not make it the responsibility of the driver.