I am a plumber and very familiar with both ABS and PVC glue, primer and all the components of the systems that are touted to weld the plastic pipe together. Quite simply it does not do as advertised. Many times in a difficult area I will simply cut the pipe off flush with the fitting hub, carefully make a saw cut through the pipe to the surface of the hub and simply peel the pipe out of the fitting.
It makes a great difference with the ABS glue on the Wing Plastic parts on how much you put on, too much and it melts the parts, too little and it does not hold. The best way is to coat the parts with a small acid brush carefully and completely and then install the parts together and let them set up for some time.
I also like to prior to using the glue and when I have occasion to do this, use a good epoxy such as PC7 and do not even mess with ABS glue. If there is room and enough body to the broken tab or post, I drill a 1/8 inch hole into both parts, then using screw, thread that into one hole, cut the head off, using the epoxy etc put it all together and let it sit. When it is set up you can simply use a small file and carefully file of any excess epoxy and now you have a post with an internal support that will stand the test of time.
I also use a light grease on the grommets and so on, and do inspect them occasionally and if they seem to be getting dried and hard, simply replace them.
Kit