Hi, Just to add, I think the Lexus documentation is all over the place and uses conflicting wording/descriptions in "Diff"erent places. The service booklet does indeed say 20K/2Yrs However, the service sheet for the guy who's going to work on your vehicles it says at 20K check Rear diff levels top up if required/ change 4th year, which would roughly be 50K if on Business User.
I have been driving now for 40 years and have always done exceptionally high milages, mainly in RWD cars and 60K has always been the norm for a diff change.