Mine seems to have the plastic pieces. On one side it vibrated very badly once we had driven it 3 hours heading home. I pushed it very hard and it "clicked" and moved up some. No more noise, and I can dump more cold air in the BR if the 5th has been closed up and it is hot. Hope my fix didn't break anything, but seems good a couple of week out...
2003 GMC Serria 2500HD - Lotsa Mods.