At the dealer, don't know what they're called but the parts guys always
know what I want when I tell them I need the plastic linkage connectors for
the wiper arms.

i have always called them wiper linkage bushings.  don't know if that is
official terminology but it always gets me the part you are asking about at
the dealership.

i used to have to replace one of these on one of me fleet trucks about once
a year.  what was causing it was leaving the trucks parked under trees and
over the course of time the area under the firewall grill would accumulate a
bunch of leaves and debris which would interfere with the movement of the
wiper arm linkage.  once i started parking the trucks in another area that
wasn't shaded by leaf dropping trees the problem has mostly gone away.

i still have at least one of these bushings in the dash of all of my trucks.
nothing worse that getting caught in a storm and finding out your wipers are
not working.  usually only takes about 20 minutes to replace the bushing and
be back on your merry way.
michael