I have the same problem, as has another member on here!
I emailed them, I still have the box and that but they told me to bring the car to their workshop for inspection. That'll do I'll just get the boat over over to England from Ireland so they can check my rail. Didn't end up doing anything about it stupidly, Should have sent the rail over to them by post.
Is the play in your rail on the right rail, where the upper and lower slider parts are connected?