I ended up emailing jefa, who in-turn sent me to their U.S. distributor. Turns out there are several models of Bavaria 38s in 2003, so I had to give them the hull number. Once they had that they could give me a diagram.
The rudder post DOES have varying dimensions, but in a step-wise manner rather than a tapered (cone) shape. The numbers on mine were 63mm main shaft, then 60 above the seal, then 50 where the shaft attaches to the pulley unit. Your millage may vary.