Nylon glides for casement style Pella or National Window

Painter/contractor says windows are quality wood casement windows in great condition, originally installed around 1980. However, the little (2")glides are worn. Although all windows are the same, we're uncertain whether they are made by Pella (due to labeling on window cranks) or "National Window" (some cranks are engraved National Window) Your help will be much appreciated! Just saw your pics below-- What a wholesome, helpful looking crew!!