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Hello everyone, I am considering detaching the pipes connected to the gearbox oil cooler inside the radiator and installing an aftermarket cooler.
My 2004 W203 M271 is reportedly prone to coolant contamination in the gearbox oil, and I believe this change might be beneficial.
I suspect that the radiator was replaced prior to my ownership, but I have no means of verification; also, installing an external cooler would alleviate my concerns.
Any information on the potential futility of my efforts, considering the vehicle is around 20 years old with 167,000 km, would be welcomed.
How can I identify an appropriate option? I cannot ascertain the contents of the radiator, making sizing challenging.
Thank you.

The simplest method to distinguish the Valeo radiator from the BEHR radiator is to examine the top right corner while facing the vehicle with the hood open. Upon seeing a little protrusion (welding seal), you possess a BEHR. If you do not, you possess a valeo.

Note that the original saddle cooler will heat the ATF when the engine coolant temperature exceeds the ATF temperature. The cooling of the ATF transpires just when its temperature exceeds that of the coolant. A distinct cooler eliminates the need for a thermostat (although one may exist in the gearbox, I am sceptical) resulting in the ATF likely operating at suboptimal temperatures most of the time.
I operate an additional cooler (original OEM fitment, supplementary to the saddle cooler) independently of the saddle cooler, although I have attached a thermostat to prevent overcooling of the ATF. I recommend that you do likewise if installing an independent cooler.
If your original radiator is functioning well and unlikely to leak, I would recommend leaving the system as it is.

Thank you; I will review it.

Thank you for the valuable insight; I have heard that if the ATF does not reach the appropriate temperature, it may not engage 5th gear (locking itself out).
The temperature range for automatic gearbox fluids (ATFs) should be between 140 to 200 degrees Celsius, according to my research. Could you please inform me of the temperature at which your thermostat opens and closes?

Mine activates around 85 - 90°C, if I remember correctly, since it is designed for engine oil. Your statistics seem elevated to me, however they may be on the lower side. I would need to do study, but I consider 140°C to be the maximum threshold. 200°C seemed very high to me

You are correct; upon review, 200 degrees is the temperature at which the oil begins to sustain damage.