Junk is probably the place where you are going to have the least odds of getting a good one , no history , in a wreck that may have pinched a wire killing it , or the last owner doing who knows what ect. .
The vast majority of [ really dead ] computers are from people doing something that kills them , like you mentioned reliable / bullet proof , also if that was the case all the time . you would not need one .
sometimes just disconnecting & reconnecting makes a connection better .
The problem is that the info & tools are harder , fewer & too costly for anyone but a high end shop to keep , then some thing I learned to do during repair is , if some went wrong , find out why , fix that 1st , then fix what broke , this is much more important with electronics because of how sensitive / or easy to kill they are .
I no longer am in the bis , so do not have a source at my finger tips , but a rebuild would be my 1st choice , this is one of the best places to get the pin check data to make sure that something in the truck is not going to kill the new unit , like the wrong wire being grounded .
The dealer is the last place you want to go , but if you decide to replace , tell the counter guy that you want to open the box if front of him [ because no returns on electrical if the seal is broken ] because you want to see if there is a check list inside that asks you to check a few connections in the harness , these are the major ones that may kill it , some suppliers do not put these in the box , tell him you do not want to pay for any with out this .
Attention: TDR Forum Junkies 
