My new thermocouple arrived (from China via eBay). I started on installing it in the back of the oven to troubleshoot what is causing the blistering.

I embedded a hook in the top of the oven to support the thermocouple. It's a piece of a stainless hairpin style cotter pin, so should hold up to the heat.

Here's a view looking up at the top of the oven showing the new thermocouple as well as the heating element retainers I recently added.