A couple years ago, Motorcycle Consumer News tested a plastic welder by Harbor Freight:
http://www.harborfreight.com/cpi/cta...emnumber=41592. They loved the thing after they learned how to use it correctly. If you are at all interested, I'll see if I can find the article.
As for the missing tab, make a cast of the whole one using clay or something. Put a similar size bushing in the missing part and place the cast on the missing tab. Then melt the plastic into the cast.