I come from the Car World. Starters can be a tricky thing. I would usually say check the brushes, but you have already done that. Is your Evo an an upgrade or did it start as an Evo? I ask to get a sense of the overall age of the Starter. The four most common fail points on a starter are in order, Brushes, Relay, Bearings, Winding.
Brushes can be a little tricky to replace. There is a little spring that holds them against the Commutator (copper cylinder on the shaft). Its usually a good idea when you have it apart to inspect the Comm for any uneven surfaces or depressions. They can inhibit the brushes from making a good connection. When installing new brushes it always a good idea to put a small dab of silicone near the top corner of the brush (spring side) to cushion some of the vibration from the engine. Vibration can damage the wire connected to the brush. You are not “Gluing” the brush in place. Just adding a dampener.
Solenoid/Relay. Pretty straight forward here. It either clicks or it doesn’t. You can check for power by putting a test light or multimeter at the harness connected to the starter (large wire connected to an insulated tab) and ground it to the engine. If you get power when you hit the switch, its not the relay.
Bearings can be tricky to diagnose. Often they are intermittent when the act up. Usually if a bearing is worn, it can cause the shaft to pull out of alignment with the brushes or bind so as not to allow the shaft to rotate. To test this, you will need someone to trigger the starter switch while the other moderately taps on the starter housing with a hard object (small hammer or medium wrench). Not so hard that you damage the casing, but hard enough to shock the shaft back into place while the magnetic field is active. Do not engage the switch for more than a second or two before allowing an equal period of rest or you risk burning up the relay. I suggest striking the support bracket rather than the starter itself so as not to damage the starter housing. If the Starter begins to spin while striking it, you found your problem.
Winding rarely goes bad except in very old starters. The internal resistance increases and weakens the magnetic field. The best way to test this is Voltage drop and Amp load. You will have to use a good known starter for comparison. On a Car Starter, it is not uncommon to see Voltage drop from near 13 V to 10.5 V on a good one. Amps varies depending on size of the motor, which is why you need to compare with a known good one.
I hope this helps you chase down your issue.