Re: Send packing the stuffing gland..
Before you think I'm down on these, I do have a dripless seal on my current boat and spec-ed it when it was built.
One boat back I did have one fail underway. I was under power and had a bilge alarm go off. Investigating I found that the donut had shifted forward on the shaft, causing the bellows to under compress. This allowed water to escape. Looked like an old rotary lawn sprinkler as the shaft rotated. Was able to shut down, loosen the grub screw, and move the donut aft, compressing the bellows. Of course, on this particular boat the seal was located under a generator, following the basic rule of boats, if you really need to fix it, you cannot reach it easily.
Since then, I've put a zinc on the shaft, forward of the donut to serve as an emergency stopper for the donut. Belt and suspenders. The installation instructions about these donut set screws are very specific, and I think I remember you are only supposed to tighten them once or replace the screws (or something like that).
Nevertheless, off I went again and put it in my current boat. Counting backwards been using them since mid 1990's with only this one failure which was probably caused by bad installation or maintenance.