There is a lot of mis information out there pro vs. con regarding dripless shaft seals.
Myth #1: Traditional seals are safer because you're not dependent on a rubber bellows.
Both types of stuffing boxes whether it be the PSS dripless type or the traditional stuffing box are 100% dependent upon a rubber hose. I have seen a first hand demonstration of a PSS bellows twisted two full turns around then let go and it sprung back to it's original shape losing none of it's elasticity. When you do this with the hard, and rather in flexible, rubber hose of a traditional stuffing box the hose will rip at less than one full twist. The bottom line is that BOTH designs are 100% dependent upon a rubber hose and BOTH of these hoses can fail!
Myth #2: The traditional stuffing box is longer lasting.
My PSS had over 2700 hours on it before I changed it and even then I found I did not need to. My prop shaft and PSS had been installed at the same time during a motor replacement. The boat then made three+ trips up and down the ditch from Maine to the Carib thus wearing out the shaft itself due to silty water wearing it at the cutlass bearing. When I replaced my prop shaft due to wear around the cutlass I ordered a new PSS but sent the old one in for testing so I could possibly keep it as a back up. It had NO wear on the stainless steel rotor and the carbon disc was like new. PSS also tested the bellows and confirmed that it too had plenty of life left in it but just because they are nice they threw in a free replacement bellows for only the cost of my shipping.
In 30+ years of boating I have replaced 4 or 5 hoses on traditional stuffing boxes and no less than three prop shafts that had been damaged by the standard stuffing box. I have yet to replace a prop shaft due to wear caused by a PSS or dripless type seal and I've now owned five boats with dripless seals. Yes, perhaps the bronze pieces will last a lifetime but so will the stainless steel rotor or the carbon rotor if my 2700 hours are any indication. The hoses however on BOTH types need periodic replacement.
Myth #3: Dripless seals sink boats:
More standard stuffing boxes are responsible for sinking boats, by a long shot, than dripless types. I got this data directly from a buddy who worked at Boat US Insurance Co.. He told me flat out that a large portion of sinking's and "total loss" claims are from leaking stuffing boxes and there was very little data on file for sinking's caused by dripless seals to compare against.
Myth#4: Dripless seals need to be burped.
While this was true of the older "slow speed" design ALL new PSS models are now vented and require NO burping. In fact for quite some time PSS would ship you the upgrade pieces to convert to a vented seal at no charge other than shipping.
Myth #5: Teflon, Drip-Less or GFO packing makes a traditional stuffing box dripless.
Even with the Gore GFO, the best possible packing material available, it still must drip some in order to not RUIN the shaft. I have experimented at length with both GFO, Teflon and the brand Drip-Less Mouldable Packing which you can read about on my web site in my article on "Re-Packing a Traditional Stuffing Box" here: http://www.pbase.com/mainecruising/stuffing_box
. You can also read my article on installing a PSS here: http://www.pbase.com/mainecruising/pss_shaft_seal
Trust me this teflon/GFO/Drip-Less Mouldable stuff should NOT be run dry no matter how hard the manufacturer try's to mislead you with marketing mis-speak & mumbo-jumbo like the difference between the phrasing "Dripless" and "Drip-Less" one is really dripless and the other just drips less..
Along with our very own, "test em hard & put em through the paces" US Coast Guard here are just a few of the builders who use the PSS right from the factory. Note the quality of some of these builder. The Coast Guard does not put anything on it's vessels that has NOT been fully tested and proven!!
BLACKWATCH (LITTLE HARBOR)
CHEOY LEE SHIPYARDS
DUFFY & DUFFY (ATLANTIC BOAT)
EGG HARBOR YACHT, LLC.
GLACIER BAY CATAMARANS
ISLAND GYPSY (HALVORSEN MARINE)
NORTH END COMPOSITES (Sabre)
RAMPAGE SPORT FISHING YACHTS
RINKER BOAT COMPANY
RIVA (FERRETTI GROUP)
U.S.C.G. 47’ M.L.B. (TEXTRON)
Gotta run I can add more insight later...