If it is a traditional stuffing box/stern gland then that does not sound good at all. If you are inexperienced with all things boaty I would suggest you get it looked at. Or post a pic on here...
I haven't seen a stuffing box like that before! I can't even work out how it is supposed to work. I'd change it for a regular style stuffing box, if I had the problem. Regarding the tube that leads from above into the propshaft tube, what is on the other end? Is it for pumping grease into the tube?
Peter.
It looks as if it is a cunning combination of stuffing box with built-in bearing. Presumably there is some packing somewhere, either in the cap or inside the other housing with the male thread on the end?
Which bit is turning? Do you mean the end cap turns with the shaft and then either tightens up or comes unscrewed, or do you mean the chunkier bronze housing on the end of the tube turns? That isn't really possible unless either its threads holding it onto the tube have gone, or even worse, the whole tube turns and something has gone at the other end.