Re: Fiberglass buildup around rudder stuffing box
It looks like that stuffing box/gland is pretty wet.. that's likely your source. The large nut needs to be tightened, and then the lower locknut brought up to secure it.
Better, though, to open the gland up and redo the packing for a new, high-confidence seal.
The link below takes you to a 'how-to'.. it's for a propshaft but it's the same job...
Re-Packing A Traditional Stuffing Box Photo Gallery by Compass Marine at pbase.com
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)