To summarize from the thread that Major Stackings linked, sounds like Acetone is the best general solution, as it melts the pieces together until they are permanently bonded together as one bit of plastic.
You only need acetone, no need for other products or ABS chips.
Just brush acetone on both pieces, join them and wait 5 minutes.
You will find that your two pieces now are literally one piece.
There is not anything stronger for abs plastic.
For the record grocery store nail polish remover is Acetone, at about 70% concentration (see material safety data sheet citation).
Cutex Regular Nail Polish Remover
Product code: PN 679 (VIJ)
Date Prepared: January 14, 2000
Hazardous Components: Acetone, Percent content: 70.0
CAS number 67-64-1
You can get 100% concetrated acetone at the hardware store, or at beauty supply stores.
If you don't mind a little extra work, using melted ABS is probably your best bet, you just need to chop up some scrap ABS into shavings (I used a big drill bit on some ABS and it made shavings very quickly), and then put them in some acetone. Play with the mixture until it comes out to your desired consistency. Make it in a squirt bottle, use it just like epoxy or whatever. This way, the entire work piece is made of ABS plastic so you shouldn't have problems with thermal expansion leading to cracks or separation like you can have with other materials.
If there isn't a tight fit though, Acetone alone might not be enough, and you can either melt a little plastic in Acetone solution to generate filler, or try other plastic-friendly glues that can both fit gaps and bond:
Right, assuming the parts that need to be glued are already a nice snug fit. Plastic welder and/or ABS sludge come in handy when you need to fill a gap though, as is so often the case in carPC-related fabrication.
I'll be experimenting with a few of these soon and will update with my results. Science!