Having ridden many years BITD with ST end levers I am very familiar with their tendency to round out the hex wrench fitting. The forming of the hex fitting is not quite as robust as a common socket head bolt. Also the threading is larger then the "one step bigger then the wrench fit" but still with a fine pitch. Add to this that few end levers were ever assembled with lube on the threads and many people didn't know which way to turn the bolt and you have a handful of reasons that these bolts rounded out.

I'll look in my stash and see if i have a spare/loose bolt. Andy.