I would give it another go with the glue and clamp. Keep repeating until the crack looks sealed. Never easy to tell when it's smeared all over the place.
Try plonking a dollop of the glue directly over the crack and let gravity sink it in. Just when it looks like it's starting to harden slightly, whip on the clamp (might take up to 4 hours to harden depending on the glue, so keep checking it). Do it in stages, doing the face bit first and then the edge. Also handy (without clamp) if you want to seal the crack flush with the face to minimise it's appearance.