Different studs could give me another 1/2" of travel on the gland nut. That could potentially save 2 rings of packing. Maybe the gland nut is not deep enough. I also need to use a drill bit to confirm the right size - what I removed appears to be 1/4", and it seems to be a snug fit as there was reasonable resistance when I removed it.
I haven't seen any GFO here, but have not looked very hard. I think I'll try and locate a shipwright to take a look at it. I do think its a bit strange to have 8 rings of packing Maybe I need to take the rudder off to look at the whole setup.