I think you've just gotten cruddy starters. Check your power and ground wires, make sure they're in good shape. You said the flywheel is in good shape, so it leads me to believe that the starters were just not good to begin with. Remanufactured, it could have been defective to start. The motor shouldn't be binding at all, and unless you're running like 12:1 compression, I doubt that's an issue.