I sold my 1990 LS400 in 2003 after driving it from new until 183,500 miles. I bought an off-lease 2000 LS400 earlier in 2003 at 38,000 miles and have driven it to about 152,000 miles. It is is remarkable condition.
The 1998-2000 5-speed transmission and the similar 2001-2003 LS430 5-speed transmission may be the most reliable and trouble free transmissions Toyota has ever made.
Does your 98 LS have a full maintenance history? Has it had occasional transmission fluid changes?
It has a decent history. A few transmission fluid changes but this one I did was overdue judging by the look and smell of the fluid. I'll bet that 2000 LS400 is a beaut.