I will not write another essay. I will not write another essay. I will not write another essay.
No, they don't blatantly show attraction to either sex, but at the same time they don't shy away from the idea of romantic relations with the few women they know (Sybil comes to mind, when she leads them to believe that she's interested in dating and both Sam and Max come to the conclusion that she means them.)
There are lots of examples here and there to assess their sexuality, but compiling it all, I'm sticking with "asexual with a slight exception for women".
Besides, as stated, romance isn't necessarily what this thread is about.