That part is normally called a fuel sending unit. It is very delicate so if time allows, you should search the forum as others have goofed it up.

If you want to see what they look like in advance, I even saw that someone has a youtube video on it (i searched for mercedes fuel sending unit). It was for an SD, so the location is different than on your car, but the part is similar.

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1968 220D, w115, /8, OM615, Automatic transmission.
My 1987 300TD wagon was sold and my 2003 W210 E320 wagon was totaled (sheds tear).