Interesting... I would be curious to see some pictures of the splotches. I've never heard of a cast iron pan needing replaced after 5 years. Mine just started breaking it at that point.
See what I mean? This was deep cleaned (using boiling water) about a month ago, reseasoned with Canola oil, and I schmear on some butter prior to each meal. I usually use it to fry eggs, and occasionally potatoes. After the food cooks, I clean it up with a paper towel.
But no matter what I do, I always wind up with this splotchy brown finish. It cooks fine, it is still non-stick, but it doesn't look like the rich black finish I see in everyone else's cast iron pictures.