2000 Mercedes-Benz S 500 Steering Squealing Noises When Turning

Squealing / Squeaking Noises From Area of Rack-And-Pinion When Steering in Both
Directions
If you receive customer reports in the above model vehicles of squealing or squeaking
noises when steering in both directions when the engine is warm, the cause may be due
to insufficient lubrication at the radial shaft sealing ring in the control head.
Note :The additive Lubrizol 6178 must only used up to a certain steering gear serial
number (see list). This restriction applies to models 203120912111220 without ABC. The
additive must no longer be used as of steering gear serial number stated below. If the
additive Lubrizol 6178 is poured into a steering gear after the steering gear serial
number stated below, damage to the steering gear is possible.
For vehicles (except Model 211) with later steering gear serial numbers from those
stated below, repair per DTB P-B-46.20/25a dated March 27, 2006. For Model 211 with
later steering gear serial numbers from those stated below, replace the steering gear per
WIS Document AR46.20-P-0600T or AR46.20-P-0600IT.
Lubrizol 6178 must only be used once in the steering system. No more than 50 ml of
Lubrizol 6178 maybe added.
Follow below steps to add additive Lubrizol 6178 into steering oil:
1. Check whether Lubrizol has already been added. This can be verified by a yellow dot
on the steering gear and power steering pump housings.
2. If Lubrizol has already been added, repair the vehicle per DTB P-B-46.20/25a dated March 27, 2006.
3. Ensure steering system is brought up to operating temperature (approx. 80 deg C).
4. Suction off 50 ml of steering oil.

Source