I have a Speedmaster which was expertly repaired by Fawaz. Upon taking it to him and explaining my problem (sporadically losing time in different positions) he popped the caseback open and had a preliminary look. He couldn't find the problem immediately, but did tell me what he would likely have to do (take apart the entire movement) and the estimated cost/time to diagnose and fix it.
True to his word, he found the problem (loose screw that was interfering with the movement) and repaired the movement while providing me with pictures of all the work he did.
I can't recommend Fawaz's work or my dealings with him enough!