That piece would be known as the foot rest (stirrup). The rivets tend to loosen up depending on the terrain you run the sled on and jumping. The first clue is usually Gray stuff emanating from between the foot rest and tunnel (some from under the fuel tank too). Thats aluminum dust and water. I'd recommend using BRP rivets or after market high quality steel rivets. Some of the factory build rivets can't be duplicated as they are pinched during manufacture. Some rivets can be replaced with similar sized aircraft high strength bolts and nuts. I have found that removing all the rivets in the assembly, cleaning up the components and gluing both the brackets and replacement rivets with good grade epoxy resin cures the looseness problem.