Lloyd, I think the blotched look comes from not wiping all of the oil over before heating it up to the 500 temp. I've had the same thing happen. A couple of times even when I thought I had done a good job of wiping it down. So, now I have two cotton towels ready. I wipe it down with one, until I'm sure I got it all, and then with the second towel, just to be sure.
Edit: also, I used to my seasoning similar to the way you did it. Now I follow the instructions on seasoning on this site. I like the results better using this method.
If you are going to put it in on 500 for 45 minutes, it's a good idea to take it out every 5-10 minutes (at least a couple of times at the beginning of the hearing process) and wipe it down again with a clean cotton cloth. Of course, if you have cleaned the excess oil off the first time time, there shouldn't be anything there to wipe, but if there is a little extra, you will get it before it bakes on.