Above the volume knob?

Yes. Silver box with small square lens.

Do you know how feasible it would be to replace?

Dunno, never done it... But rule out the software thing first before worrying about that.

When you get your serial cable, upgrade it to the latest 2.0 version, and install hijack, and use its "Button Codes Display" feature to see if any ir signals from any remote are beeing seen by it.