A lot of plastics parts are marked to show what type of plastic it is so look to see if there a symbol on there. If you have access to some MEK (methyl ethyl ketone) or methylene chloride you can rub some on the plastic with a rag. If the rag melts the plastic then you can use that solvent to repair the part. if it doesn't melt the part than it's probably polypropylene or polyethylene. If it's any type of poly you will need an adhesive called Plexus to make the repair. http://www.itwplexus.com/

For abs repairs I'd recommend the ABS cement from Marsh Laboratories in Pittsburg Pa 412-271-3060. It's really inexpensive and is sold in 1 pint cans.