First,Where you abide.Do the authorities use SALT on Winter roadways?
Second,Your MB has a Corrosion Protection installed @ the Factory on both
the Engine compartment and the underside of the suspension.
Third,the FSM calls for Re-Installation of the Protection AFTER each engine/
underside CLEANING.

BUT,the Best CLEAN is attained with P21S applied and then "Tooth-Brushed"
BEFORE rinsing.
CAUTION! This will remove ALL "GUNK" as well as all the MB applied Protection.
(You will want to have Chemical Proof Gloves on your Hands!) AND Eye Protection.

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'84 300SD sold
124.128