Also (4) in the rear suspension illustration, is this something that wears out? or.............? What purpose does it serve?

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BMW X5 4,6is
Black / Imola Red interior / Titanium trim
22'' style 168 - 9,5 front / 11 rear
Eibach 40mm lowering kit
30mm H&R Spacers
P53 Headlights Org Xenon, angel eyes & auto level
Alpine Sub
Roof Rail Delete
AC Schnitzer Rear spoiler
AC Schnitzer Pedals - Dead pedal - Fire ext - Emg brake - Gear knob
AC Schnitzer Emblems @ Steering wheel, front, rear
AC Schnitzer ECU - Trans - Exhaust

Ferrari 360 Modena