You can try to tighten the packing nut a little to see if that stops or slows the leak.
Before that, how much is the box leaking and is it leaking under power when the shaft is turning or when it's just sitting there and the shaft is not turning? A few drips a minute when the shaft is turning is okay. Even if the shaft isn't turning, a few drips a minute isn't catastrophic.
A few weeks ago mine was dripping at rest once every 11 seconds and every 2 to 3 seconds when the shaft was turning. I snugged the packing nut down a 1/16 of a turn or so and the drip rate reduced to one every 45 seconds at rest and once every 6 seconds when the shaft was turning; good enough for me. My packing flax is 6 years old, so it may have to be replaced at the end of this season.
If you do decide to tighten the packing nut, remember you need to loosen the locking nut first. You may have to apply a little liquid wrench stuff to loosen any corrosion. Also, don't over tighten the nut. If your not getting a few drips a minute when the shaft is turning and the shaft/stuffing box isn't remaining cool, you need to back the nut off a little until it does.
The link the Sailingdog gave you of Halekia's technique is very a excellent tutorial.