1991 300 sl needs plastic frame that goes around headlight assembly.

 

common issue. Auto Parts at AutohausAZ - OEM Auto Parts - Discount Replacement Parts, Resources and Car Care Tips under "Body, trim & lighting" then "headlight cover/door" that's a good buy, I paid $70 each ten years ago. use a plastic uv protectant after installing. mine still looks like new. sunlight is an enemy to all plastic and rubber parts.

 

I'm ordering parts today. Do you know where I can order passenger headlight bucket?
Thank you for your assistance.

 

if you're talking about the housing. there's one at ebaymotors for $35 under "mercedes r129 headlights"