Looks like sometime in the past, that RX spent some time off road. Meaning either bottomed out or went into a ditch and had contacts with some hard surfaces with it's undercarriage.
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​​​​​No big deal as long as there are no suspension damages and no critical component damages (leaking oil pan or transmission​ pan, and etc.).

 

Gene great information!!! I also have used fluid film and I think it is easy to apply, economical, readily available and seems to do a great job! I live in Georgia but my 2010 RX 450h, spent most of its life in Mass and it also has lots of undercarriage rust but after using the fluid film it seems to have perhaps arrested the rust. I will just keep an eye on the rust and keep using the fluid film!!! Thanks! Tim

 

Rust protection is a must if you are planning to keep the car for more than 10 years. Canadian winter is very bad for cars. I had a 13 years old Kia Sportage and after 13 years the rust eat thru the bottom frame without rust protection. I have an RX350 2015 now and just had Krown rust protection on it. I'll probably apply the rust protection every few years. It doesn't cost much anyway. Lexus build quality is alot better than a Kia but still.