I did my aerial today, it's easy peasy really, right, LS400 i presume>
1. open your Lexus toolbox, there are 4 bolts, 10mm, undo these.
2. Remove Plastic Boot guard which runs just inside the boot across where the boot cath is.
3. Remove Carpet around toolbox, the tool box and it's surrounding carpet should pull out easily.
4 You should Now see the aerial,
5 Disconnect the aerial and the power wires, this is easy, also there is a little cylinder thingy at the bottom which just pulls off, careful you don;t brake the plastic ball holding it in place.
6 when looking at aerial you should see 4 bolts, undo bottom 2.
ok now to the outside of the car.
7where the aerial extends from the boot, the is a metal circle with four grooves in, this tweists off, you can use a screwdriver to ease it round, just stick the flat edge in a groove and push, don;t slip, you'll scratch ya paint
8 The aerial should now be free, take it out and put the new one in.
If you buy one from halford I suggest you take the broken one with you to check connections.
Hope this is of some help
Bison :zee: