You aren't missing anything, no; the Replacement Red Lens for Optronics MC32RB and MCL32RB Trailer Lights # A32RB is exactly what you need as a replacement lens for either the Optronics Trailer Clearance or Side Marker Light # MC32RB (Incandescent) or # MCL32RB (LED).
This is the correct lens, though it will snap on so it will be somewhat tight; using a smidgen of force will snap it on. view full answer...