I don't know the part number for the ignition switch for a 2004 but I just checked the parts manuals for my '06 and '09 and they are both C0152.1AD BODY, electrical, ignition switch. From that I assume the '04 is the same but we will need someone with the earlier parts list to confirm.
I am also assuming you are referring to the electrical part not the mechanical part? The mechanical part differs between models.
If you do mean the electrical part then it may just need cleaning. At around 80,000 Km '06 developed some issues that required fiddling with the ignition switch to get a good electrical connection so I ordered new switch but while waiting for it I tried pulling it apart as a temporary measure. That was completely successful and 18,000km later I still haven't replaced it.
One you have removed the switch assembly (Tamper-proof T45 Torx needed) you can remove the end of the electrical switch with a couple of small flat blade screwdrivers - you can see the plastic arrow-head latches in this shot:
You can pull the switch apart and not have pieces go in every direction - the contacts are clipped in place. In this shot you see some green corrosion on the upper set of copper contacts. Clean all of the contacts (I used Methylated spirits and a Scoth-brite pad) and re-grease (I used some silicon grease I had at hand and that has worked OK) and then re-assemble.
Let me know if you need more detail.