I copied the following off one of the forums or mailing lists, but I can't remember which one. Applies to a 617, but has some applicable info for your oil cooler, I believe. It's interesting that MB even offers this replacement part (screwed nipple). Whoever came up with that name?
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The correct metric size is 27mm or you can use 1 & 1/16 inch. Be very careful removing the oil lines from the oil cooler. The threaded nipples on the cooler are soft aluminum and will strip or gall easily. I replaced my oil cooler lines last May. Despite slowly working the coupling nut with lots a penetrating oil, I still galled the threads on the cooler. A new oil cooler is $300. I planned for this and expected something like this to happen. I bought new threaded fittings for in between the oil lines and oil filter housing because I expected the old fittings to strip when I took them off the line couplings. These fittings are less than $5.00 each. I reused the original fittings so I have an extra set now. All I had to do is cut the aluminum threads off the oil cooler, drill a pilot hole, tap new threads, and install the new fittings. The thread tap size is 18mm by 1.5mm. The drill size for the pilot hole is 21/32 inches, I don't know the metric equivalent. It took a local machinist 15 minutes to cut off the aluminum threads back to the nut part, drill the pilot holes (there's plenty of metal there), and tap the new threads. It took longer to rinse out all the aluminum filings and grit out of the cooler than it did to work on it. Here are the MB part numbers for the threaded oil line fittings and copper washers. MB Part # Description 915013-013002 Screwed Nipples (That's what the label said.) 007603-018101 Ring, General, Metal "
After reading this, I ordered two new "screwed nipples" to have on hand from the dealer and they are copper fittings that were not unreasonably priced. FWIW
