Update: Thank God I found some spare O-Rings at my friend's local autoparts store. Funny thing, I brought my headers with me to 4 different muffler shops and they had no f*in idea what I was talking about (even after physically pointing at the "groove") when I mentioned gaskets. Idiots

 

Maybe they were confised with the gasket term and expected to hear a crush gasket/washer??

I had to pick them up for my old CL-S and the first muffler shop I went to knew what it was.