Steve D'Antonio, who wrote "The Amazing Mr. Moesly" article in the literature section, did a big article on stuffing boxes in the Jan/Feb 08 issue of Passagemaker magazine. You might be able to find it by going to their web site at passagemaker.com. I remember him saying that while those dripless systems work great as long as the engine feeds them a continuous supply of water, if they DO fail, it's not always graceful, i.e. they can sink your boat!
He mentioned some concerns about twin engine boats when they were run on one engine. I guess it's the type of thing that if you left boat in water, you'd want to get into the habit of checking the stuffing box to make sure it was still dripless before leaving the boat! I believe they use a carbon face seal (a carbon ring that's spring loaded against a very hard and perfectly flat plate that rotates with the shaft), like those used in your car's AC compressor. That carbon ring is very brittle, and if it breaks, which is rare, you could be looking at a fairly good leak! I view those things as a classic example of "better" sometimes being the enemy of "good enough"!
