I model in P4 18.83 mm gauge and some older makes of plastic-based track would become under-gauge, especially on curves. I cut the outer sides of some of the chairs, allowing the rail to move outwards very slightly, and then I was able, just, to insert a track gauge. The application of a soldering iron for a few seconds allowed the gauge to set to the correct value, and a few drops of superglue secured everything,
Definitely works for me.
John