I am not familiar with the M104 engine, but I did own a '82 300 Turbo diesel and my current '84 380 SL.
I purchase my lines, rubber and plastic, in meter lengths from my local MB dealer. Keep in mind these items are metric diameter sized. As well, stuff you can buy at the Zone (not metric sized) may work or may not. You may want to remove the hose line and take with you. Also, you may need to cut a bit off the end to get the true dia. of hose.
Remember, some German engineer was paid to figure out the correct dia. of the hose line, plastic or rubber, to insure the proper functioning of the operating part.