This might sound lame, but I have repaired cracks in abs plastic by melting it together with a soldering iron. It was a clean break and didn't need repainting, so I repaired it on the inside and got some scrap abs from tap plastic to melt is as filler.
not lame at all,....your only the FIRST person to realize "hey, I can't epoxy this, maybe HEAT WILL WORK"
you now know how to plastic weld,......HF makes a little welder for about $35:
http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=41592
try that next time instead of the soldering iron, and they make ABS weld rods.
I like this one as you don't need a compressor, as it has it's own air supply so it's great for "off site" work:
http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=96712
sometimes the plastic is a composite, that is, several plastics mixed together, on those it will ONLY STICK TO ITSELF, so if you need some "weld rod", you are forced to scavenge the rod material from an un-noticible place on the part you have, or use another scrap part for rod. note: you must get ALL the paint off of any scavenged piece to use a weld rod, plastic only sticks to plastic, not paint.
it's not very well known, but you can get VERY STRONG BONDS with ABS using MEK, a type of solvent, but the parts need to be clamped while curing for about 6 hours:
just get both edges of the break wet with mek, wait about 30 seconds, then push the edges together, you should see some molten plastic ooze out from the break, which is a good sign you have melted both edges, now you just have to clamp, tape, or brace, the break to maintain that pressure as the MEK evaporates, which takes about 6 hours. this ONLY works with ABS, and ABS+PA (abs+nylon), the MEK will not melt any of the newer TPO(thermo-plastic-olefin), or PET(polyethylene), or PP(polyproplene) type composites, like acerbis motoX stuff.
once dry, the MEK bond with be about 80% to 90% of the original strength.