There shouldn’t be any there. You can see in your photo the remnants of the High Temperature threadlocker that lulzbot uses to seal the heater block to the bore tube. They generally place a very liberal amount, tighten to specification and wait for it to cure. This makes essentially a high temperature gasket on the threads going From the top of the block down about 5-6mm worth of thread. Even if it is applied improperly, to have leakage from that location if the nozzle is also installed properly is rare.
What you are probably seeing there, is a whip of pre print nozzle ooze that managed to get stuck on top of the block. Those strings of plastic tend to contract as they cool, and can sometimes anchor themselves in weird places, where they proceed to cook and then char. I would remove that bit with a pair of pliers, see if it comes back right away and proceed from there. The only way you are having a leak at that location is if the bore tube itself has a hole in it. That isn’t unprecedented, but it is an extremely extremely rare occurrence.
If you had 3 nozzles fail in the exact same manner, something odd is going on.