Sorry I know I'm bumping an uber old thread here...
I own an IS300 and encountering similar problems to you in regards to the rear carrier (or knuckle) bushing that connects to the lower control arm which is the same piece you're talking about here in this thread relating to your LS400.
In any case, I did some digging into Armstrong and they seem to sell the IS 300 Rear Carrier Bushing.
Can anyone provide their input on parts from Armstrong in terms of quality relative to OEM and whether this has solved their suspension problems?
Thanks!