I would try solvent welding. If you need filler, grind up some compatible plastic with a file and mix the filings with solvent. It will meld with the original plastic and make a very strong bond. Just don't spill any solvent, that stuff will instantly mark anywhere it drips. The stuff I have is Methylene Chloride, it's sold for welding acrylic but it works well on ABS too. Plumbing cement for ABS pipe ought to work too.