Hi Jake, so Lexus have taken a look but not resolved the issue - right...
Are your disks scoured at all?
Is the vehicle new to you?
Do you know when the pads were last changed?
Do you know when the calipers were last lubed? - the rear have sliders are notorious for drying out and dragging 😉 Oh and dealers typically don't maintain/lube these, they just let them get so bad that they then charge you to replace the whole rear calliper.
Do you brake hard to engage the hydraulics are just a little/medium to use the motor regen for most of the braking?
I'd have a look at RockAuto over in the states for a ride height sensor. Is it just the arm that's broken? - if so, then you can make up a rod/rose joint yourself to fix it 😉
Regards, Lee