When you turn off the ignition in your 99-00 LS400 does the steering wheel groan and move in short jerks as it returns to the top position? Mine does. :( When there are guests in the car, it's down right embarrassing (e.g., "at least my Mercedes doesn't do that!"). I just bought my 2000 LS 400 in August and have been attempting to work out some of the bugs.
My Lexus dealer said that the behavior was 'normal', that I was just being fussy. I looked it up on <http://www.alldata.com/products/diy> and found that there was a Techincal Service Information Bulletin (TSIB) on the subject <#ST003-00 published by Lexus on May 19, 2000>. The warranty period for this fix has expired and it appears to be a rather extensive and expensive fix. But, if the problem bothers you, you may want to look into the TSIB.
FYI, my discriminating and courteous Lexus dealer is busy denying that the TSIB even exists. (The next closest dealer is 30 miles away.)
NOTE: To access data on alldata.com requires a subscription fee. This TSIB is the only item of any real import relative to the 2000 LS400s.