hi welcome to the Ls400 Forum
The cambelt and waterpump should last at least 100k miles and 10years or so ! No rush then for that I guess ( was the waterpump changed ? )
You don't give us the reg no. for us to DVLA check the MOTs etc
Nor tell us what work has been carried out etc ... the UCAs are relatively expensive to replace and OEM is best for longevity second time around, be it from Lexus/Toyota UK or Amayama or Rockauto supplied ( Blueprint are ok but don't have the longevity ) ............... I guess Lexus have replaced them all by now as you say it's had all Lexus stamps for all work, the originals probably wouldn't have lasted 200+ k miles ..... so that's the huge expense out of the way for another 100 / 150k miles
The exhaust tends to blow and on mine, three times now over 220k miles, it's been welded at @£40 a time
The wheels always go poor but at least you don't need them looking good to have a serviceable car, nor that scrape fixed for £300 ( seems a lot tbh )
Enjoy the most wonderful motoring money can buy ....... this Mk3 I've had 8 years and just under 100k miles, but this is my third Ls400, a Mk1 and a Mk2 and been my main car for some 18 years ......... wouldn't change her for the world
My second car is a 56 plate Honda Legend which now had for 3 years approaching and 20k miles in my gf's driving ...... I MUCH PREFER my Ls400
Enjoy
Malc