It looks to me like hard rubber, not plastic. And, the look of the pad cups indicates it may be a Pruefer Silver Throat under a different name. In that case, very much worth fixing!
The liner tube began with Pruefer production from 1940 to about 68. It's brass, plated to look like German silver. Presumably, it makes it play louder, and also makes it impossible to break the center tenon. It was marketed mostly as a student step-up, but is also well-regarded by jazz players. There are some other message threads on Silver Throat.
Is it hard rubber? Dip a cotton tip in acetone and rub a hidden spot of the body like the end of a tenon. If no black comes off, it's rubber, not plastic. The bell looks like plastic, but not original.