Leochick

I recently replaced the radiator on my 2007 E350. It was a simple enough job, the only issue I had was not properly reconnecting the tranny oil cooler line. I was able to get the coupler on, replace the transmission fluid that was lost when I started the engine, and I guess I lost the O ring in the process, because when I drove the car the next day, the hose came out, and I lost both the plastic coupler bush (sleeve) and all my transmission fluid again. I ordered another coupler bush and O rings but this one is not fitting on the radiator like the last one. It's like it's slightly too small for it?? Do the coupler bushes come in different sizes and I bought the wrong one? I've been looking around and can't find any information to support this thought process. Can I change out the fitting on the radiator to a slightly smaller size? Is there some trick to getting it on that I'm missing? I haven't been able to drive my car in weeks and the fact that this seemingly small task is taking up so much time and effort is draining on my psyche. I'd rather not have to take the radiator out again, but I'm at my wit's end. Any advice would be helpful.

Edit: The Radiator purchased was a CSF 3428, including an image of it and the coupling bush, it's marked with a "5" so I'm unsure if there's another size?

Coupling Bush... Not sure if that's the actual name for the part.

Radiator
The lower line is the problem. Everything else fits/ is working perfectly. So it's weird to me that this one part is causing so much trouble.

tjts1

Typical Chinese aftermarket radiator problem. A. Mercedes proprietary connector sucks. I simply bypassed the radiator installed a separate transmission cooler.

Plutoe

what is your day job!!