Hmmm...you buy a product that you can't use unless you remember a code.
Ostensibly this was to serve as a theft deterrent, right?  Now what thief
studies radios to see which ones might have a code lock, BEFORE coming back
to steal yours.  Not many I would guess.  They just bust in, steal the radio
destroy the dash f*ck up the rest of the interior and then throw the radio
away when it can't be used.  Some deterrent, eh?  Dump the ancient
heidleberg, get a reno or aspen if you like the casette and remote and aux
input feature.  Or even a Jackson. Cosmetically matches the instruments and
dash, FAR outperforms the heidelturd, removable face, tons of other
features.
Adaptable easily to the A series of changers with built in changer controls
already in the head unit.  Gimme a shout if you need more info on this.
Yah, you're going to sell the car, but enhancing the sale with a better
radio might be worth it.

cheers,

pensioner