The missing shim was probably an issue for the last starter. To check the bendix pull the starter and watch it move in and out. Not all rebuilts are done correctly. The starter has to be bolted down securely so it will work correctly.
Use a DVOM and check the wire to the solenoid. With it unplugged put the meter on it and make sure it turns on and off. A bad ignition switch or ignition relay can work some times and not work. If you have a 12 volt test light watch it as somebody else is wiggling the switch. If this is the problem check at the ignition switch and relay if it has one. As I'm not their I can only suggest different problems. For your shim at least cut one from some thin metal. A purchased shim will cover the flat spot where the two bolts go in to bolt it down. I worked on one with my mechanic and it took 30 or more trys before the ignition switch failed. We took it apart after installing a new one and it had burnt contacts.