Antenna Problem?

I have a 2005 Mercedes S500 that had my Sirius radio installed at the dealer when I purchased the car in November of 2004. It has worked flawlessly since that point (until now) working well with my sound system that was factory installed in the car. About two or three weeks ago I noticed that the "aquiring signal" warning was coming on the screen as the sound went off with this just happening for a few seconds at a time and lasting longer as time has gone on where this will now happen for days at a time. Given that the antenna which is one of those magnetic rooftop antennas is now over 5 years old, is it a reasonable conclusion based on other' experiences that perhaps this is the issue? I don't mind purchasing a new antenna which brings me to me second question, is it fairly easy to replace? I thank you in advance for your help and look forward to your replies.

As a side note, the existing antenna says on the bottom of it: Sirius 6111001100 if that helps determine the correct replacement item.