The gasket was probably in there in you just didn't notice. sometimes they blend in with the opening and are difficult to see. As was said without a gasket it would be popping so bad and running poorly that you couldn't ride it. I just bought new OEM gaskets yesterday and I was surprised to see that they were copper crush gaskets. Unlike the Felpro gaskets that fit but have a short life span. I think The OEM gaskets are worth the extra couple bucks if they are readily available to you.
Curt, you sure are typing fast today.