I too had an all-plastic kinetic (Midway), bought in the early 90's. Used it rarely over the last 10 years, and when I finally needed it, it broke, same as yours.
Replaced with an RCBS kinetic. Figure I can live with the expense if it fails in 10 years.
ANYTHING plastic, over 20+ years, will become brittle and fail.
Plastics become brittle because of manufacturing costs. Volatile plasticizers are less expensive than permanent plasticizers and volatile materials will, over time, outgas from the material leading to brittleness.
If you've got any cheap toys from the 80's and 90's, I'd bet they are getting very brittle.