When your starter contacts go it usually exhibits the same symptoms as a bad battery. Slow/No cranking sometimes intermittently.
LarryB offers a kit to remedy and upgrade the starter.
Heres what the original plunger and contacts look like.
Comparison of the contacts oe vs larryb’s
This is what the new larger contacts look like installed.
While I had the starter apart I also changed the brushes on my starter motor.