Originally Posted by Larks

At ace hardware, home depot, etc you can buy little brass thread inserts. I have tried different brands like Threadserts but I prefer the brass ones made for wood. Basically you have to drill the hole larger and thread the insert into the plastic. It will only work where there is a lot of plastic but I have used them before in a jam with excellent results. In fact my 8T has 2 in it now that are holding the chassis to the bulk (diff gearboxes).

here is what they look like...