This is actually on a 07 Taurus 3.0 Vulcan, but the question is valid with trucks also.

Last month I replaced the timing cover and when I had the starter and oil pan off I noticed the flywheel ring gear was kind of rough so I replaced the starter at that time since the starter gear seemed a little loose.

Fast forward to 2 weeks ago when my wife called saying it is grinding and not starting. I turned the engine a little by hand and it started fine. I tried starting it over and over and fine. I took the starter off and the ring gear has a bad spot on it with less than 1/2 teeth left, but the starter still looks brand new. I assume the damage was already done with the old starter.

I can see on the starter marks where the gear engagement looks good. I assume it is ok and had it tested at Autozone and it tested ok. The only question I have is there is a brass bushing in the nose that seems loose and can move up and down. Gear and shaft have no play - the bushing moves up into the nose and if you shake it will come back down. Autozone guys have no clue of course since the testing machine said pass, and I think it is ok, but don't want to chance the gear if it could be this starter.

On a side note, I got a new pioneer brand flex plate. It has a 1/8" variation where the gear was not set and welded evenly around the flex plate. I ordered and will pick up one at Ford today and hopefully all will be well with that one.