Hmmm. You don't turn JC off before pocketing the 4?I love the K4, but I'm tired of the wet hands and leaking in my pocket. I've replace the #16 o-ring and all the others below the tank to no avail. Until I can order and install some 12x1.5mm o-rings I've cranked my old K3. I'm enjoying leak free vaping again. There's less flavor, but more satisfaction without the leaks. If the K3 leaks it's because I put my finger over the air hole and created too much vacuum. That's my fault.
That said, I will order some larger o-rings and see if that fixes the problem. I'm also using less juice with the K3 and that's a plus.
I always do since I think bouncing around in ones pocket will slosh the juice around pretty hard and cause extra juice to be forced into the chamber.
I turn JC on and off about 50 times a day while at work. Works like a champ and NEVER had a leak, so far at least.
Good luck though.