Through the process of elimination it appears that 23nm is the answer for the drain plug. Use that information at your own risk though and I'd like to have the official value from Porsche themselves.

My process for determining this was to start at 15nm and attempt to tighten some more, then advance by 1nm until it stopped clicking. That brought me to 24nm. Backing down to 20nm again I then used the same process to attempt to remove the plug and 24nm was again the answer. So the process of elimination leaves me reasonably confident that if I use 23nm I should be fine.

EDIT: I have since seen the "WM 1001IN Tightening torques for engine" document which says the proper torque is 22nm.