I have a 87 560SL and recently put the battery back in after winter storage. The radio was never removed. However the radio now shows the "dashed lines" on the display which the owner's book indicates is due to an anti-theft device. I believe I have the code in the owners manual for the radio. What steps do I need to do to reactivate the radio?

Is there a way to avoid this in the future?

 

Dealer has a tool that plugs in to the radio after the faceplate is removed, it resets the radio. There is no code to punch into this early type of radio.