I thought I would post this for posterity in case someone in the future has this problem. Plus I wanted to share a "DUH" moment with everyone.
I took my starter apart to clean and inspect. I forgot to mark the end plate which holds the brushes. I reassembled it by guessing. On first use, the drive gear sounded like it was stripping the little ratchet gear with a "ZZZZZZING" noise. I struggled with it for a while until I finally realized the starter was turning backwards!
Finally I pieced together in my head what must have happened. I discovered after trial and error that I installed the end plate rotated TWO bolt holes off.
But I know now that if I need a starter to run the opposite direction, it's not hard to do.
Starter runs backwards
Moderators: rickf, raymond, Mr. Recovery
Starter runs backwards
1967 M151A1