A starter solenoid kicked my butt on a 1998 Civic for 4 hours

Had a 98 Civic in bay 3 on Thursday that would not crank, just a single click every time the key turned. I did what I always do, went straight to the battery first, then the starter, pulled both, tested both, all good. Spent 3 hours chasing grounds and even swapped the ignition switch from a parts car before I slowed down and really looked at the signal wire. The connector had green crust inside it where I could not see, and the voltage was dropping to 6.2 when the key hit start. Twenty minutes with a pick and some dielectric grease and it fired right up. Back when I started in the 90s we could check most stuff with a test light and hear the problem, but these older cars hiding corrosion in the plugs still get me if I rush. What is your go-to move when a no crank passes the parts cannon test?