The Audi TT LCA rear bushing is solid, rather than skeletonized (webbed) the
way the Golf/Jetta/GTI one is. It's less flexible than the OEM bushing, so it
improves steering precision and input.
Audi parts 5Q0-407-183-L & 81A-407-183 cross reference, but might not be
as stiff (but still stiffer than Golf OEM)
These make a huge improvement in the way the car tracks, handles bumps
(especially in corners) and even shifts. (because torque applied to the
wheels when releasing the clutch with vigor doesn't upset the alignment)
You get all this without any added NVH! (Noise, Vibration, Harshness)
Installing them requires a hydraulic press, there's no way you're going to
install them into the control arms with a bench vice or hammer and drift.
Removing them is easier with press, but can be done with a sawzall if you're
careful not to damage the control arm.