Radiator fluid seems to be leaking from the radiator hose cap, and the fluid looks just a bit milky (like a little oil got in it). I was wondering if this was common and it means something more than just needing a new radiator hose cap gasket dealy, sorry if I'm not using the technical terms, I'm tired.

 

In the rotary, it is very difficult for oil to get into the coolant. Replace the cap to see if that solves the leak. Leaking fluid will often leave a white residue where it drys, so are you sure that is not what you are seeing?

 

It didn't get a chance to dry, I saw it leaking green coolant from the hose cap, and in the resevoir for coolant it looked a little milky. What about the leak? Just the gasket or something worse?

 

Sonds like the leak is the rad cap itself (from your description...). It could be the gasket, or a cracked housing.

I think the first thing you need to do is completely flush the system, then drive the car for a few days and see if the "milky" colour comes back.