The 300E uses an electric antenna made by Hirschmann. From 1992 on, the antenna was a Hirschmann 6000EL. Like the rest of my 300E, the antenna is easily serviced and parts are readily available.

One day, I noticed that my antenna no longer extended when I turned on the radio. "Hmmm, Must be the mast.", I said. The mast has a long plastic toothed 'tail' that engages a gear inside the antenna mechanism. Commonly, this tail breaks. The repair is simple. A new mast is about $50. To remove the old antenna, unscrew the nut, turn the radio on, and PULL! (carefully note the orientation of the gear teeth as the old antenna comes out). Shove the tail of the replacement antenna down into the opening formerly occupied by the old one, and have someone turn the radio off while you guide the new mast gear into the motor.

However, when I removed my mast, the entire tail seemed to be intact. Uh Oh.

That meant I would have to remove the antenna mechanism from the car and see if it could be repaired. Surprisingly, the whole job turned out to be rather simple.

The first thing to do is to locate the small molding on the left rear quarter panel that supports the upper end of the antenna mechanism. In the photos below, you can clearly see the large nut that must be removed.

Next, open the trunk and remove the left fender liner. Here you can see enough of the fender liner has been pulled away to expose the antenna mechanism. The mechanism is secured by a single screw. Remove it. Unplug the antenna and electrical wires, and the mechanism can be moved to the workbench.

Here is a picture of the mechanism with the cover removed. After cleaning out the grime, I found my problem:

The key on the left gear in the photo below was broken. (The tip of the screwdriver points to where the key should have been.) The gear on the right is driven by the mechanism's motor. The gear on the left engages the teeth in the antenna mast's tail, and its rotation is locked to the right gear by this key. No key, no rotation, no antenna movement.

The second problem is that the small metal roller (pointed to by the tip of the screwdriver) has a groove worn in it. I suspect that the grime inside the mechanism jammed this roller, keeping it from turning.

Here is a better picture of the roller:

Now for the good news. Every single part of the antenna mechanism can be purchased from this guy:

Walter Odemer Company, Inc.

Here is an exploded view and parts list on his page for the Hirschmann 6000EL:

http://store6.yimg.com/I/walters-store_1739_241439

I probably spent 50 bucks on parts. Five minutes after the parts arrived, I had the entire thing put back together, installed in my car, and working.