TLDR: I discovered that the pre-FL Bi-Xenon projector assemblies are directly compatible with projectors made for a BMW 3 series. Specifically the E92 or E93. I found a bolt in replacement from RetrofitLab with the item name:
"BMW 3 E92 E93 07-13 bi-xenon headlight repair & upgrade kit for D1S D3S headlights AL headlights"

My projectors were corroded/burned and the light output was so bad it was actually hazardous to drive at night. While looking for replacement W204 projectors, I found that nobody seems to offer projectors for the pre-FL model. I found an eBay listing for the projectors and started reverse image searching from there. Most of my results returned listings for BMW projectors that had identical reflector bowls with slightly different lens and beam cutoff assemblies. After this discovery, I decided to crack open my own headlights to find a part number, and sure enough the reflector bowl, which is what bolts into the headlight housing, was the same.


From there, I turned back to new replacement/upgrade projectors and discovered that RetrofitLab and a few other companies offered brand new bolt in projectors. After comparing my various options, I pulled the trigger on the RetrofitLab projectors because they had the most similar looking lens and also the electrical connector for the high beam cutoff solenoid is the same as what's in the W204 headlights. After a wait for them to ship from Europe, I got to make the final comparison and install them in my "C550" project.

The new projector is on the bottom and burned OEM is above it.
After a quick comparison, I decided that the RetrofitLab projector would bolt right in and completed the installation for both headlights.
The difference is night and day with the new projectors. For the first time in my ownership of this car, I have been able to see more than 100 feet in front of me and can actually make out details on the road surface more than the reflectors down the middle of the road!
There are a few advantages to going this route. It's significantly cheaper than buying aftermarket headlight assemblies that tend to fade rapidly and have generally poor construction. Also, you can maintain OEM nice to have features like the automatic leveling and active corner turning on cars like the C63. It also keeps the OEM look for the headlights, which I like since the rest of the car is visually totally stock to make it a "sleeper" with the only indication of what's under the hood being a rebadge on the trunk.

The before/after is a bit misleading. The old projectors were super diffused from dirty lenses and the burned reflectors, so they appear to output more light in the picture. The RetrofitLab projectors do have a slightly narrower beam, but it's a dramatically improved light output in that beam with a very crisp cutoff so you don't blind oncoming traffic. Additionally, in the before picture I had attempted sanding off the burned layer and polished the bare aluminum underneath. I did this to the left headlight which did help light output, but it still struggled to send light down the road and was super diffused. The results were alright for a free solution, but a doubt the improved output would last long as the bare aluminum would be more prone to corrosion.

Before:


After:


Thanks for reading this post, and I hope it helps anyone else who's having trouble with worn out Bi-xenons!

 

Fantastic work — all of it! Thanks for writing up such a detailed report of your investigative work and modification journey. I’m glad to hear that you were able to not only keep the OEM look, but also improve upon it with Retrofit Labs’ stuff!

I bet this is gonna help someone big time in the future.