Weak starter, 98, 40 hp Tracker Force

[Toonman]

Starter engages but weak, barely turns motor. Disassembled, cleaned, sanded armature with carberundum cloth , heard that was bad, sprayed out with contact cleaner. Checked for continuity, none. Brushes look almost new. Pulled over 325 amps at motor ground wire. Voltage drops to 9.5 when trying to turn over at starter sol. positive lead .
What do I need to check before replacing ?

[Elbo]

Take your spark plugs out and it should spin freely.If it don't then it will be an engine issue.Put your plugs back in and see how the starter handles the coppression load.

[Elbo]

Also clean your battery connections and make sure the battery is full charged.

[Toonman]

Battery is fully charged, motor will start turn over and run very good when starter does it's job. As I said at the starter my voltage only drops to about 9 1/2 and I am showing a 360 amp draw therefore I believe problem must be in the starter. How can I test Armature windings and other possible issues?