Ok, so in in the process of finding the best way to repair these items. Other than the usual drill holes at the end of splits, and the odd bit of filling, I have tried resin, epoxy,sealant, super glue, heat gun etc. Most of these plastics are ABS type, and you can have some success using ABS shavings by dragging a sharp blade across a waste bit , and mixing the shavings in suitable glue, then pasting it on the appropriate area.
The crux of the operation is to clean the area with a decent de greaser. Grind out the affected area back to the naked plastic, which in my case is black, although the painted article is white. De grease. Then heat the area slightly with a heat gun, then get yourself a glue gun. This heats up a long slug of plastic to its molten stage, then apply.......Its brilliant. Do a few runs of the stuff, builing up an area of glue, whether it be for splits, broken lugs, affixing studs and its very strong, having tested a few dummy runs.
As for filling, get yourself a flexible filler, the normal car body stuff peels off.

 

For small repairs I use Plastex.

My bike is held together by Plastex repairs.

I sometimes use some wire mesh as reinforcement and build up the plastex around it. I've recently used it for the tabs in the tail unit that the screws go through, which had cracked all the way through. I also used it to create new tabs with holes through them at the bottom of both halves of the fairing at the very front of the bike, which had broke off completely. And for where the lower fairing screws into the upper. And for one of the tabs on the fuse box cover. And...
It's great stuff. Comes in red, black, white...

 

ABS cement, the stuff used for joining ABS plumbing, will also work on our fairings. I used that and a sheet of ABS from Parts Express to rebuild my fairings.

I've also used a product called Q-Bond, which appears to be similar to Plastex, with good results.

 

Q Bond, absolutely swear by it if applied correctly. Flexible filler for final shaping and ready for paint!
Cheers
Peter.