The Problem with the 109 S Altimeters (+/- 100ft in light Turbulence Indicated) is an error introduced by the new Pitot location.
In the old location the static port was located on the underside of the Pitot tube. Now the pitot has simply been rotated 90 degrees and planted on the side of the nose, the static port is inboard and in-between the Pitot and the Nose section.
During small pitch changes there is a pressure change in this area which causes a significant pressure area in the static system, hence the altimeter errors.
This can cause difficulty flying accurate indicated altitudes in light turbulence.
I guess this is also why the Autopilot has fun as well!
But it is a GREAT machine!!!