My PSS seal vent leaks
at high prop revs even though it is 2 meters long. My solution was to plumb it into the cockpit
drain. On reading the instructions it seems that it can be blocked off on a sailing boat as its only really needed for planing boats.
I always break the carbon seal with my hand before staring the engine
if I have not used the boat for a while. I seem to remember that this is suggested as after a period of no use, the seal welds itself to the stainless hub that it runs against.
Just a thought .... is the cutlass bearing more worn now and letting in more water