They should have been made of Delrin or maybe even graphite filled micarta.
Nylon is definitely not up to the task in a dirty environment.

 

Plastic bushings wouldn't last a NY minute. All versions of these bushings since 1957 have been nylon.

 

Are you suggesting nylon isn't a plastic?

There are a lot of plastics (like Delrin/acetal) that ARE formulated and produced just for bushings, bearings and other low friction ridgid parts that won't cold flow or distort like nylon does.

[Url] https://en.m.wikipedia.org/wiki/Polyoxymethylene#Development[/url ]

https://en.m.wikipedia.org/wiki/Nylon