Command navigation does not retain addresses; what are my options?

Command does not save new address and none of previous addresses are there. A new address is there as long as vehicle is not turned off.Mercedes dealer wants to replace the whole unit for $4500.00...seems to be common problem on these years>>7 model years affected: 2000, 2001, 2002, 2003, 2004, 2005, 2006...