My 1985 300D had a broken mast when I bought it. Ordered a new mast and seal. Got all installed, but discovered the antenna was erratic up and down. Took it apart and saw that the gears were good, spring inside the gears was fine but belt was loose and worm appeared to be worn on the center teeth that contact the worm gear. So my quest began to find a new worm. While waiting for some info from some folks who deal in Hirschmann Repairs, I decided to further investigate. I took the motor worm assembly off and discovered the plastic inserts that the worm shaft bushings ride in was cracked, powdered and pulverized. Carefully lifted the metal spring tangs that hold the plastic and bushings into the frame. Through a little trial and error, I discovered a solution. With some rubber tape (I used some orange rubber elastic wrap, similar to electrical tape, but only sticks to itself when stretched, similar to F4 tape for anyone who has ever worked military aircraft). Cut the width to match the width of the metal bushings and wrapped 2.5 inches of tape tightly around the bushing. From there I set the taped bushings into the carrier and reinstalled the metal tangs. Set the belt back on and secured the motor. Put it all back together and it's working like a champ. Unfortunately, I didn't get any pics of this. But anyone who attempts this repair will see that it makes sense as they get into the antenna. The part number for my antenna is 2018200175, and the motor assembly is 721 073 001.

Hope this helps someone in the future.

Regards,
Mike