I'm looking at a 2001 Lexus LS430 UL package with 148,000 miles on it. It seems to have all the bells and whistles. My concern is with the overall reliability of the LS430 vs LS400. I have seen quite a few posts about the air suspension being problematic. Is it guaranteed to fail on these cars? What else needs to be looked after on an UL?

 

Lots of posts on air suspension issues over the years. Certainly;y not guaranteed to fail but definitely a relative weak point on cars with this option compared to other extremely systems on the car.
On a UL especially you have to meticulously check every single switch and button and option to make sure they all work. Check mirrors, steering wheel adj motors, audio system for blown amp and speakers, underneath for rust and exhaust leaks, engine/trans fluid leaks/seepage. That's about it