My perfect solution is throw it away
. That's always been my beef with things becoming plastic. It don't rust or rot, but when it breaks it's trash and you can fix rust and rot. But, people are clever and I have seen some plastic fixed and don't some myself. No glue would work on early pliable plastic because it was parafin based. In my old camper the neck to the water tank was cracked and it wouldn't draw water to the sink. The PO had attempted a repair gluing part of a milk jug over it. I had a guy impress me with his repair (I was out of state on a trip). He took all the glue of with a wheel, then cut 1/4" of the end of the neck. He cut that in two and used that as welding rod with his soldering gun. Same plastic welds same plastic! This didn't have to be pretty like something on your dash, but that tank pumped good the rest of it's days and I learned something. I've welded plastic like that since.