Mine started doing that after 22 years. I used a remote starter switch(out
of gear hand brake on) and starter worked everytime.I then pulled off the
plastic cover at the steering column and wiggled the switch that feeds
power to the starter. The starter would work. so.... it was the switch
replaced switch no mas problem. It is a good idea to check your battery
post clean them and the water level in the battery. If the battery is
really corroded you should pull it out and clean underside too. Reinstall
with battery protection paste. Voltage will leak from battery with dirt
and gunk around it.  Good Luck.

84 West Tiico Ol'Paint