If thae batt is up/cables cleaned which I'm sure they are since you've been on this, if you firmly touch the large/small terminals with a large screwdriver & it dont crank then yes the starter is the culprit. Just be careful not to touch the metal case. A nice display of sparks down there tells you that you have enough current to the starter & also have continuity on the ground side between the starter case back around to the batt neg post but the starter itself ain't functioning