I found that post before and tried most of what was said. as for this part:
"Symptoms: Turn on headlights, have someone watch while you turn key to start position and then back to off. If headlights are bright, go dim in "start" and then go bright again in "off" - you probably have terminal resistance. (Headlights are bright because there is 12V and they only need a few amps; but the starter motor pulls 300+ amps, so the lights dim and the motor won't turn, because the corrosion is choking off the current.)"
My headlights do dim when you turn the key and get the one click. But the voltage to the on the battery doesn't really drop (maybe by less than 1 volt). The voltage on the solenoid drops off from 12+ to less than 3 volts so it seems.
I haven't tried this yet:
" Diagnosis: Disconnect battery cable, test continuity with voltmeter, one probe at solenoid connection (or frame ground for the ground cable) and the other touching the inside of the connector. Should be 0.5 ohms no matter where you touch the inside of the connector. Corrosion will increase resistance and you will see this right away in the voltmeter readings."