My only real concern with the nylon is how it will react to extreme hot/cold temperatures. With the way that it is mounted, it is simply squeezed between the wiper arm and the round metal bushing/sheath that goes between the shaft and the retaining nut. The nylon piece firmly holds the arm to that bushing, and the bushing itself is what allows it to rotate within the range of the slot that I made in the arm.

And if the nylon does melt or become brittle from exposure to heat/cold/climate, then I can use a brass or steel bushing next time.