I lost the caps to both my headlights after switching out the bulbs for LEDs. I switched back and wanted something to replace the caps. It's an extremely simple model that works as-is for normal filament bulbs but is customizable in case you need longer (like I needed when I switched to LEDs - you would want to add a hole for better air movement - version uploaded marked “LED” is untested).

I believe the Smart part number for the original cap is 4518260324 or 451-826-03-24.