Quite a few of the older Merlins crack at the STI Bosses. The reason is simple. The weld area of the boss is too small, and it's welded in the highest stressed part of the tube. It's why a lot of companies now weld the bosses to the head tube. Also, I'm not a huge fan of the bullet ends - much prefer the Wright style dropouts, for the very reason shown above. Nice of Litespeed to reweld it for you, though.