Strange wear on distributor drive gear
 

After replacing the intake gasket on my 99 Blazer it still ran horrible at 1000-2000 RPM and I was getting an error code for a timing problem. After setting the timing 2 times with no luck I read on here that the distributor drive gear is a common problem. On one side of the gear the teeth look like new, but on the opposite side the teeth were worn most of the way through. I put the new gear in and now it runs great. The SES light went out instantly.

My question is: what would cause the uneven wear? Is my distributor shaft bent? Bad heat treating on the gear? I just bought this Blazer a few weeks ago so I don't know have any history on work that was done before I bought it. Right now my plan is to drive it a couple of months and then check for wear.