Leica USA service is different situation altogether, as they are the only source for repairs for digital gear, and they didn't put any of revenue from their exorbitant prices into improving their service departments; instead, they put it into a fancy headquarters. Simply unacceptable for a premium brand to have such ridiculously poor service.
As far as DAG goes, he not only has 40+ years experience, he has a test equipment collection that no one else does: proper collimators, shims & magnification optics, lenses made of tool steel by Leitz, infinity targets, 1 meter test stand, etc. etc.