My recent experience: They've only been back in the car for a fortnight, so I can't comment on durability. I used a product called No More Gaps. It's a water based gap filler for building use. Cleans up with water and is paintable and can be sanded. There's gotta be something similar outside Australia.
One of these should work. PASCOFIX Strongest Super Glue CA Glue Crazy Glue Super Glue Ceramic Super Glue for Metal Glue for Plastic Repair Glue Shoe Glue Strong Glue for Plastic Epoxy Industrial Super Glue Rubber: Amazon.com: Tools & Home Improvement JB Weld PlasticWeld Syringe 25 ml USA Plastic Weld 50132
I'm an original JB weld guys myself. You can fill athin bit in the gap, clean well and the JB releases perfectly from regular masking tap. Only drawback is long cure time. I've never used a powered colorant but I think it would work great. Good luck