Try Purple Power cleaner, safe for all plastics. Jeff Coleman

The FRA also refers ladders as stiles and treads made of wood, iron or steel. Jeff Coleman

AAR Field Manual Rule 79 Lists Ladder Treads. Ladders complete, includes two side rails or stiles and treads. Rule 83 Qualifer PE, Ladder Tread Qualifer PD, Ladder Stile Bracket Jeff Coleman

This is 50T Gon. series 71000-71674 built by Bethlehem Steel in 1934. Jeff Coleman