well you can actually use ABS model cement on the plastic interior parts.
Tenax-7R Liquid Model Cement works very well in making a bond.
you can also re-enforce the plastic parts with sheets of ABS plastic.
alternatively you can use plasti-fix which is like a 2 part plastic epoxy it uses microscopic beads of plastic that melt with a liquid glue so you place the powder where you want and then hit it with the liquid glue and let it dry and sand to shape.
you can also use a 2 part epoxy that binds to plastic.
another option is to use a Crazy glue formula designed for bonding plastic, then you can use a fiberglass mesh on the back side and use CA glue on it and make a very strong bond and re-enforcement repair.
i used the Tenax-7R on my car to bond the A-pillar cracks since you can lay the glue with capillary action if your careful you can make a almost invisible repair
and you won't even need to paint the part after.
one issue with the plastic this old is it tends to turn back into powder you can use the Tenax-7R to try and stabilize an area that is disintegrating, since it with get sucked into the powder and start to melt it back together, then you can try and recreate the area shooting it with a high build primer then wrinkle paint and finally paint to match the interior.
of course its never as great as a fresh part but sometimes you have no choice. krylon fusion paint is good on high wear interior parts it will melt the surface of the plastic slightly and bond must stronger.
i would always test any repair method you try first on an area of the part that is not visible just to make sure there is no surprises.
