Suburban Roof Rack Cross-bar Sliders

[Dejablu311]

I ordered what I assumed was an original roof rack off ebay. I unwrapped it when it arrived and everything looked great. It wasn't until I went to install it 8 months later that I realized I am missing a pair of the plastic sliders (no clue what they are called) that are used to hold the cross-bars in place. I have spent hours trying to track them down online without any luck. I went to the local chevy dealership and the parts counter was no help. I was hoping someone on here can at least confirm that what I am talking about exists and provide a part number.

 

[yevgenievich]

Not a very good picture, but could you identify pieces that are missing?

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[Charlie]