Even though the additional information would have prevented us posters from heading off in the wrong direction of diagnosing a starter-related problem, the suggestions posted may help others, whose starters are the problem. Not a waste of time or knowledge sharing.
In your case, the best thing you can do for your starter switch is what you have done so far: disassembly, inspection and cleaning, followed by a careful re-assembly. Ensure that no parts are rubbing against each other, which will affect the plunger return action. Make sure the brass strip is not installed ****-eyed and that it will travel the full distance without rubbing against the sides of the metal switch housing. Some repo strips are too wide and have very little tolerance for side-to-side misalignment. Check the plunging action manually by pressing on the switch's rod receptible several times. It should spring back easily without any hesitation. The rod receptible should not be floppy loose, nor tight in its bore.
Also make sure the starter rod is not getting stuck inside the firewall's rubber grommet. For some reason, all firewall grommet holes have been made too small for decades. They usually need to be reamed out a bit and lubricated. Try spraying some silicone lubricant on that firewall grommet to eliminate it from the list of possible starter switch hangups.
Marshall
