Unfortunately the majority of SIEMENS/VDO codes (including your CDR 2005 ) will NOT be available for free (or cheap) from anywhere on the Internet as access is required to the original factory database...which is not commercially available..
Try your Main Dealer or a Decoding Service or your local Car Radio / Audio Shop (who are normally the cheapest option) who will connect it to a laptop to read/recode the memory chip (EEPROM)
You will find very few , honest , on-line decoding services that will be able to provide this VDO code by just quoting the Serial Number as no SIEMENS/VDO database is commercially available apart from the original factory database held by the Main Vauxhall Dealer.
The only honest Decoders that can offer this are the larger Professional Services ...those with access to this Vauxhall database ( and I only know of 1 Decoding Business that has this access ...and they charge £25 )
The risk is that if any quoted code does NOT work , then there will be no refund of any money.
If I were you, I would TAKE the radio into a Decoding Service (such as your local Car Radio store ) and let them connect it to a laptop to read the actual working code inside your radio`s memory chip (EEPROM) using special software. That normally costs around £10 > £20
At least it will work after you have paid your money