firstly let me just say that i have learn quite a bit about UMDs from this forum. Now that i've decided to onw one, i need some advice from you guys. The e39 model i'm presently looking at is a 520i yr 2001. Some issues with this car. Noticed from the registration card that the engine number has been changed. When I enquired, was told that it was changed by auto bavaria within the 2 yr warranty period due to the previous owner's complain. Just wondering what might have happened to warrant changing the entire engine and whether this something to worry about? I have seen a copy of the service invoice for the engine change by AB. Fyi, car is said to be accident free.The other thing is the radio in this car does not seem to work. Is this something that can easily be replaced and if so how much would it set me back? Is the radio linked to any other electronic devices which i should check out?Appreciate any input you guys can give me. Thanks in advance.