I, too have gotten to be a pro and putting the car in neutral, ebrake on,
turning on the key, and "jumping" the solenoid from under the
car....can(seriously) accomplish this in less than a minute.

I went thru fixing this problem the right way and it took half a day and
patience.  I disconnected the wire at the ignition switch that sends power
to the starter when the switch is turned....then I put 12 v to that wire,
inside the car.  If the car did not start...............told me that it was
either wiring or solenoid (already new less than one year old Bosch starter
so ruled that out)  then, I hooked the wire back up inside the car, went to
the starter with a voltmeter, disconnected same red wire with black stripe
on the starter, and had someone turn the key

12v or more............solenoid bad.

less than 12v wiring issue.  (test voltage at battery to see what should be
max flow)...........On my car there was a splice in the wire where the
previous owner tapped in for a radio that was corroded.  I replaced this
span of wire and all is well.

Sometimes, it is as simple as a new crimp terminal being put on the end of
the red wire w black stripe that goes to the solenoid.

PS..............I have gone the relay method, the new solenoid method, etc.,
and found that it was truly worth the time and effort to spend a half day to
understand this system.  Now if it does not start I will be surprised.