I have a second-hand Prusa i3 MK3S with a Bondtech extruder upgrade and what I believe is an E3D V6 hot end. Does this look like the gold version? Would that have a copper heat block? How would I check? It seems the heat break clogged, so I dissassembled the extruder and the hot end. I was able to unclog the heat break by pushing the lump through, but now I'm wondering about re-assembly and possible parts replacement. The threads on the nozzle were covered in a white/gray substance that I'm not sure belongs there, and the nozzle doesn't thread freely into the heating block as-is. According to the assembly instructions, there should only be heatsink compound on the cold end of the heat break. I freed the hot end of the heat break from the heating block, and it too is covered in the same substance. I'm a total n00b at this, so please be gentle, but I'm wondering: Could this substance be heatsink compound and/or perhaps boron nitride? The stuff is dry and hard/powdery. Is it safe/sane to run a tap through the heater block to clean up the gunk? Is the nozzle reusable, or should I just replace it? This is a second-hand printer, so I have no idea how much time there's on this nozzle. Is there any reason I should change the heat break or the heater block? What, if anything, should I use for heatsink compound on cold end of the heat break? Should I worry about something for the hot end and the nozzle? Does anyone offhand recognize the thermistor and/or the heater in that picture?