I have 2 Oil Cooler Hose endes that I modified so I could use pressureized Air to test the Oil Cooler. But, I doubt if that is an option for most People.
Removing the one from the other Car seems to be the best option except that removing the Oil Cooler Hoses often resuts in a stripped Nipple and that could happen to either one of the Oil Coolers if you remove them.
Details on how to try to avoid stripping the Nipples when the Hose is removed can be found below.
Repair Links
DIY Links by Parts Category - PeachParts Mercedes ShopForum
PeachPartsWiki: Do It Yourself Articles - Mercedes Vehicles