Starter Problem?

[DT1]

Hi guys,
I haven't been very active lately, but I have been on the forum every day. It seems like every time I decide to leave some input on an issue that arises, someone beats me to the solution. I guess that's what happens when you join a forum where there are so many knowledgeable people.
Now I have an issue of my own and I could use a bit of feedback.
The other day I got in my truck to go on my daily ride and she wouldn't start. When I hit the ignition, all I got was a "Click". No problem. Probably a weak battery or a bad connection. I turned the headlights on high beam and they were nice and bright, so for good measure, I turned the fan on high. Everything was a go but still no ignition. The battery was putting out 12 volts so I cleaned the posts and cables and checked the ground. Still no ignition. I pulled the battery out of another car and jumped it with the truck battery and it finally started. With the engine running the battery was at 13.5 volts so the alternator checked fine. I shut the truck down and it immediately started. I have been driving it for about a week now and it has started every time. Then, yesterday I had the same problem and had to call my wife to come and jump start me. I'm thinking that it could be a worn starter brush and every once in a while when I shut the truck down the starter rotor lands on that "Sour spot" and won't turn. Before I remove the starter, I'd like to know what you guys think.