To reduce windshield wiper blade chatter on 1983 Century a four (4) degree twist to the blade attaching end of the wiper arm has been incorporated into production the fourth week of March, 1983.
The new arm assemblies (20467903 & 20467904) can be identified by a "4" formed into the under surface of the wiper arm die cast base as shown in the illustration.
General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.