Okay, so it turns out the parts diagram above is for the HAP1. Weller just incorrectly put it onto their US page for the HAP200. Apparently according to the European distributor such errors are common.
The element T0058737701N (for the HAP1) can be ordered but only from Europe. In the USA your only option is to send it back to Apex who offers a flat rate exchange for 25% less than MSRP or about the same price as you can buy a new one online

The Euro site has the correct parts diagram for the HAP200 and the element is "5 87 617 43" but T0058761743N is not orderable anywhere.
Lesson learned? Avoid Apex Tools. Buy Hakko.