Right then ... Bad GPS antenna.
You have some options, go to dealer and hand them several hundred pounds for an OEM antenna and installation
Go to Ebay, breakers yard or the like and find a used unit and install your self, will be around 100 pounds.
Get a 10 pound Chinese active antenna with either a blue FAKRA right angle connector or WICLIC connector ( depends on where you want to plug it in )
and place the antenna under center headrest on back parcel shelf. Run the coax cable along top rear of back seats to passenger side, along bottom of C pillar to rear of parcel shelf finger pushing it out of sight, thru steel shelf under parcel shelf into trunk ( you will need to pull the paneling in the trunk ) and either plug directly into back of Nav unit ( blue FAKRA connector ) or into break point on drivers side in trunk hinge area.
Will not work as well as an external antenna but should work well enough
From another thread >>
A cheap fix is a $20'ish active GPS antenna with blue FAKRA connector, preferably a right angle one. For the dollar conscious amongst us, look here GPS Active Antenna for all GPS devices with Fakra Blue connector
Note the picture shows a straight FAKRA connector, you must specify in the order a R/A ( right angle ) FAKRA C type connector. 3 meter long coax. They have free shipping and you can use paypal. The company is located in Shenzhen China.
For those preferring a stateside vendor ( at least the phone number is 212 NYC area ) look here http://www.mbdoctor.com/mercedes-ben...s-510-002.html
Also has free shipping and uses paypal.