Johnstone has had success in reducing water dripping into the boat via the shaft packing. And this despite the conventional idea that some minimum drip rate needs to be present. He is probably successful because he is skilled in a broad variety of shaft packing in many applications not just marine. Anyway his method is to slowly creep up on packing compression thus he reduces drip to seep - but that does not mean that water is not present in the shaft packing interface. Also he uses a teflon impregnated flax - different from plain vanilla flax.. . . a rotating proper with a standard flax packing must have water drips to lube the shaft , 2 to 10 drips terminate with shaft turning. 'getting away without any leakage when running' is a TERRIBLE idea , it will damage your $1000 prop shaft.
When the packing is installed one initially makes the packing nut just hand tight - then one subsequently makes very tiny subsequent compression adjustments to get the packing to seep but not drip. I copied Johnstone's approach and replicated the same results.
Once thing for sure - there is very small margin between too tight and too loose. You do not need to guess because that can be verified with an infrared thermometer.
Charles