Antenna

Hello, a familiar problem.
At the antenna hole at the rear side it oxidises around.
The original antenna from Audi is defective and I want to
Corrosion eliminated is a normal rod antenna for unscrewing
assembly.
Beru offers some, I looked at some, but they fit
from the bracket not and in my opinion the foot is also not compatible with the aluminum body.
Someone already has a suitable ant. - What's up?
I am grateful for every information! Gerd