I designed this on Tinkercad. My first real useful design. I was replacing the headlights on my 2003 GMC Sonoma (S10) and one of the retainers was missing. So, a few minutes in Tinkercad, and here I go. Fits just fine. It's a little thicker than the factory retainer, but fit quite snug, so will also eliminate some of the highlight wiggle.
Its about 114mm long and 29mm wide

This worked for the 2003 GMC Sonoma, but the same part is used on many Chevrolet, Buick, Olds, and GMC vehicles

Simple print, just use 100% infil. Supports are not needed

I have only tried this with ABS, but other filaments may be better suited. PLA would not be recommended as if you live in a hot environment, they would probably deform.