Simon, I've tried for several days now, on 4 different computers and 3 different ISP's, to view the picture of the stuffing box that you were asking about on June 19 but can't get the picture to come up on any of them. I can't see any pictures posted on this thread after the one June 17, so can't make any comments.
However, here is a URL which has diagrams of several submarine stuffing boxes for periscopes, which might be of some help.
If I add it up right, there should be about 7 stuffing boxes on a type VII U-boat
(1 each for the arm to activate the forward dive planes, rear dive planes and rudders) total of 3
(1 for each of the 2 propellor shafts) total of 2
(1 for each of the 2 periscopes) total of 2
About the only difference is that the propellor shaft stuffing boxes would have to stand up to longer periods of use at higher speeds, but other than that, they would probably be very similar in design.
On my boat, I can't get at the stuffing box very easily since it is buried deep in the keel and I have to dismantle the panels on two berths and then dive in head first to get to it in a very confined space. My owner's manual doesn't have a diagram either.
However, the principal of them is basically the same except that most modern stuffing boxes seem to be only of metal with no wood (lignam vitae). The stuffing box is filled usually with oiled rope or cotton, packed very tightly and then with the pressure increased by turning screws that condense the packing as much as mechanically possible. As can be seen in the URL I've posted, there is sometimes also a bushing formed by a flat wire or grooved tube wrapped around the moveable shaft to allow water-repellant lubrication to service the shaft as well.
Hope this is of some help.