You should be able to just eye ball them to see if they are bad. if they are all dried up and not sealing it's time to replace them. I used the loctite ready gasket stuff on my lights to make sure they were good. It's less than 20 a can and did all my roof marker lights with one can. Just two beads around the bottom of the light and it expands into place. I'm not sure about the clips, you might check gmpartsdirect.com they may have them.