Associate principal trumpet Glenn Fischthal and principal percussionist Jack van Geem both retired from San Francisco Symphony at the end of the 2011-12 season. The orchestra will be holding auditions in January for both positions.
At the beginning of December, the Chicago Symphony announced that David Herbert - our principal timpanist - has been appointed their principal timpanist, effective July 10, 2013. Presumably we'll have auditions for that spot as well, at some point, though it is often the case that a departing principal player is considered on leave for the first year of a new job. And goodness knows, sometimes it has taken MTT a good long time to replace solo players.
Oh - read the fascinating comment thread to the Slipped Disk posting linked to above about David Herbert.