I'm losing about 12oz of radiator fluid every two weeks. Doesn't show up on the ground and isn't coming out of the exhaust (No fluid out of the tail pipes and exhaust seems about the same) and the engine is running ok.

Is there anything BESIDES a bad head gasket that could be causing the fluid loss?

it's a 97-Z28 with 177,500+ on it (gotta update the sig)

 

How does the oil look, does it have a milky appearance?

 

No. If anything it's a little darker than usual but I'm coming up on my usual oil change so it might just be dirty.