Those under tray bolts and clips are a bloody pain in the bum. I cant understand their thinking (that's assuming they were) using steel bolts and clips mounted on plastic parts in an area exposed to the elements and needing to be removed regularly for maintenance!
Most of mine were damaged during garage servicing and they used ty wraps to hold bits together on completion. I've since renewed them all, some needing to be drilled out, and plastered them with grease.