I have the Euro Rails on my car and the flatter OEM cross bars. When I put on the cross bars I can slide them around after i tighten the bolts. The cross bars rubber seems to be hard, is there any way to replace the rubber that contacts the rails? I tried just putting electrical tape over the old rubber, and that worked for a few uses, but I would like a more permanent solution.

 

I had the same problem, I bought a 3mm thick silicone rubber sheet and cut some new pads to shape. I left the original rubber pads in situ and placed the new cut pads between them and the roof rails top and bottom. It's solid now and doesn't move Link to silicon sheet on eBay