The Mercedes Ignition Cylinder (called "Tumbler" in the rest of the industry) has
"Leaves" of metal instead of Tumblers.
The Mercedes Keys are STEEL ...No Metallic fragments from keys to clog up the
Cylinder internals.

WD40,PB Blaster,Etc.,Etc.,Etc. are all petroleum type TEMPORARY Lubricants...
The "Carrier" (VOC like liquids) evaporate quickly,Leaving a sticky Gummy ,Varnish like remainder.


EDIT: Wrong,Wrong,Wrong Again !

Please see Max Bumpo's REPLY # 6 to this post:

"1) Get a can of the official MB cylinder lock lubricant, cost is ~$10, it has a key-shaped application tip on a pressurized little can so you get all the lubricant exactly where you want it. It lubricates and protects against freezing."

Mb Part# 001 989 26 51 10

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'84 300SD sold
124.128