Just how important is the antenna grommet? Pictures of the ugly truth.
 

These pictures are of my recently acquired 1990 300D 2.5Turbo. Hidden under the trunk lining below the antenna is a horrid example of what can happen if water leaks in through the grommet and the liner traps the moisture against the metal body. This cancer will require cutting out and welding in new metal, which unfortunately reached painted surfaces on the outside.

Oh and yes, I have a new grommet.

http://i284.photobucket.com/albums/l...o/DSC00197.jpg
http://i284.photobucket.com/albums/l...o/DSC00198.jpg
http://i284.photobucket.com/albums/l...o/DSC00199.jpg
http://i284.photobucket.com/albums/l...o/DSC00200.jpg
http://i284.photobucket.com/albums/l...o/DSC00201.jpg

I think that's probably the worst case of a previous owner not paying attention to what is happening with the car. I've never seen rust that bad in any MB trunk. It takes a long period of neglect to get to that stage.
Keep an eye on your trunk, replace that grommet, and be OK. Hope you can get it fixed without a second mortgage.

I'm so glad I don't live in the rust belt! But as d.delano pointed out, that rust has been working on it for awhile! I've never seen a W124 rust there before :(. Do you think it will need an entire rear quarter?

This is nothing new in my home country. Has more to do with the drain being plugged.

Here is the follow up on this problem.
http://www.peachparts.com/shopforum/3382965-post60.html
and
http://www.peachparts.com/shopforum/3382967-post61.html

I went out to add some beeswax to the sealing surfaces of the grommet. That rust is plain nasty.