We've had both... installed a PYI dripless on a boat with a V-drive - appreciated the feature given the almost impossible access to the SB below the oil pan. It worked fine, but anything that disturbs the sealing pressure from the bellows will allow leakage. If you plan to do in-the-water gearbox changes, or engine removal be sure to take precautions to avoid unloading the seal - it will leak very well indeed!
1984 Fast/Nicholson 345 "FastForward"
".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)