My just-purchased ZHP's head unit has a FUBAR volume-on/off knob. Getting it fixed would be as expensive as simply replacing it with an Ebay unit. If I do this, does the new one need to be coded by the dealer? Any other issues or is it (hopefully) just plug & play? I see one now out of another '05 (critical because I want to keep MP3 compatibility, and I believe '05 is the first year) for < $200 that I'll jump on if it's a simple swap. Thanks.