If you are referring to the antenna that looks like the stock SLK with the flexible part cut off, then there is an SLK version that is just screwed in place of the stock mast. That is the European version of the antenna. You can order it online, or possibly from a Mercedes parts department.fitty_six said:
A word of warning, if you live even remotely far from the source you will notice a significant decrease in signal. I live 30 minutes outside SF and I lost half of my stations. I ended up reverting to the stock antenna.