Unfortunately, after a few days, the seller informed me that he could not find in his warehouse the oil line no. 3 that I had bought, so he refunded my money.

However, it turned out that this corroded section of the oil line is part no. 2 in the above drawing, not no. 3.
Interestingly, I managed to buy this oil line no. 2 yesterday, new, and to be precise part no. 05099379AA in a Polish store.
It cost me $33 including shipping.
I thought this part was impossible to get...
Today the courier delivered it to me - here it is in the photo below. I hope it will fit.



I also bought these used oil lines pulled from a Mercedes SLK320 (R170), and trying them on by eye, it turned out that they were the same oil lines as in my car.
This offer was missing the final section of the oil line, the one at the radiator itself, but I managed to buy it new in a Polish store, as I mentioned above.