When you say 300TD I am assuming it is a station wagon.

http://www.peachparts.com/shopforum/showthread.php?t=154459&highlight=fuel+screen+lip+dave

This post shows the difference between the sedan and wagon fuel screen.
The fuel lines are connected at the front of the wagon tank. There is a separating plate between the main body and the fuel output lines that the screen inserts into. The lip on the screen divides the two sections. So installing a bar may be difficult to get it to effect the outer panel only, depending on where the dent is located. Consider getting a used tank from the junk dealer. Or just living with the dent

If the car is the sedan then what SD Blue said is correct.

Search function.
As you learn the various parts of the car you will improve your search function. For the link above I inserted "Fuel screen lip dave" in the search window. I know that it was my post, the "dave" I always sign my posts, Dave. I also know I wrote "fuel screen" and that I wrote "lip" That is how I found it.
If I wanted it specifically for the sedan I would have added that word in the search.
You can also go to the advanced search and link just the diesel discussion.

Dave

PS Go to the "user CP" at the top of the screen and fill out your signature. That way we know what car were dealing with. Just as my signature shows. I just have to specify which Mercedes I'm talking about, which I usually put in the title of the post

__________________
1970 220D, owned 1980-1990
1980 240D, owned 1990-1992
1982 300TD, owned 1992-1993
1986 300SDL, owned 1993-2004
1999 E300, owned 1999-2003
1982 300TD, 213,880mi, owned since Nov 18, 1991- Aug 4, 2010 SOLD
1988 560SL, 100,000mi, owned since 1995
1965 Mustang Fastback Mileage Unknown(My sons)
1983 240D, 176,000mi (My daughers) owned since 2004
2007 Honda Accord EX-L I4 auto, the new daily driver
1985 300D 264,000mi Son's new daily driver.(sold)
2008 Hyundai Tiberon. Daughters new car