To install the motor first place the ~1" long adapter bushing over the end of the shaft. Next insert the shaft through the hole in the cab. Place the rubber seal over the protruding shaft followed by the specially shaped washer which conforms to the cab profile. Finally install the chromium plated nut on the end of the shaft to hold everything in place. At this point the wiper arm can be installed.

Those attaching parts are available but do not come with the wiper arms.