Hey, A little hard without seeing the damage, but there is an epoxy that I use that you can get at Lowes or a home depot, called 7 minute epoxy. (don't let that fool you) it does set in 7 mins but i would at least give it a full day or 2 to fully cure. It is a two part epoxy that you have to mix, once fully cured it is hard even for a chisel to chip the stuff. Now you can create extra stength if you take your soldering irion (yes just any old soldering irion will do) and melt the plastic together first before applying the epoxy. When doing any of this though, make sure both parts of the plastic are clean, I use a dremel to clean the plastic edges first(use soapy water if you have to) before starting ANY mending process. If edges are not clean you will repair until you wear the skin of your hands. This is probablly THE most important thing to do before starting, especially as you said you have used other adhesives on it previously. I would try these things, and see how you go, otherwise i would find someone to weld them for you, I would offer but since you said you were not in my area, you may not want to send your plastics.
Let me know how go. Feel free to email me for any further questions Boomy3200@yahoo.com