Hello Royston,
I don't know what lubricants you have tried, but I do know that some (especially oil based lubricants can adversely affect some plastics. Companies like Lakeland, Kleeneasy, often sell plastic curtain track cleaner and lubricant this might be a better, but you will need to clean off any other lubricants first for best results.
Alternatively talcum powder can be an effective lubricant on wood to wood (draw runners) and some plastics but again the surfaces need to is free of other containments