I've had good luck with solvent welding. I think the stuff is mostly MEK, it's sold for welding acrylic but it works on most ABS plastics too. Just be careful not to drip it anywhere as it will melt and scar whatever it gets on. I use a small syringe with a needle to put just a few drips right where I want it. Wicks into the crack and melts the plastic back together.