http://www.ultimatereef.net/forums/s...d.php?t=133096
It will probably only leach a little rust into your tank but why risk it IMO.
I would clean off the rust & add a light coat of silicone or something over it to keep it from rusting in the future.
I'm just not a big fan of letting things like rust get into my system if I can help it. It may not hurt anything, but then again it may. JMHO.
Anthony