Lost Red Plastic Cover on ST-E2

A few months ago, I bought an ST-E@ remote transmitter to use with my 20D and 580EX.

I notice today after a shoot that the red plastic cover on the AF-assist beam emitter has fallen off and is now lost.

Does anyone know how I can replace it? Does it have a real function? Can I just put a red plastic gel where it used to be?

Thanks

does it still work? I think all you have to do is call canon and order a part.

The transmitter still works. I'm just not sure if it will have any effect on anything. I emailed Canon this AM to ask about a replacement part.

Thanks

the red light helps focusing in the dark. Because red is more sensitive to the AF sensor, and is able to give contrast just about whatever you shoot that red beam to.