Even once it sets, it will still work for a long time. If you have some of the bambu paste, that also works fine for an experiment. We may even find that the nozzle heats faster and is more consistant with the lcd readout temp because you obviously had a gap. It almost looks like the temp sensor sits slightly higher than the surrounding heater, in your pic
Try running something small and flat across the face of the heater and see if it snags on the sensor
Sure, but where is the sensor? Can you circle where it is that I should probe?
There really is no need for thermal grease. The printer was designed to work without it and it might throw the temp off as it was calibrated without it.
I believe its this part. In the other pic, you can see that this area is cleaner. In my mind, that means it was riding on this sensor, with a gap around it that allowed that gunk to fill it. Too bad we cant see nozzle heater output % at all times because i bet the heater was struggling. I would have used a spring behind the sensor to apply pressure instead of trying to cut it this close. Not saying you should, but if this was mine, I would lap it with wet sand paper on a piece of glass or something small enough to fit in that gap
Fair enough, but is there a better way to avoid the gunk build-up and eventual sticking of the nozzle to the mating surface?
I went and checked some of mine for you. This is what I found. I do have a tiny bit of leak by on a couple. Definitely seems like theres something wrong with yours. I would say, maybe the nozzle wasnt seated, but it looks like it only had good pressure against the sensor.
The nozzle itself feels fairly flush. However, the mating surface may be another matter entirely:
If so, would this necessitate a replacement of the entire printhead? Or is there a replacement for just that part of it? Looks like it may be held on by 3 bolts.
Not sure, would have to figure out why its happening and where its coming from in the first place. I swapped my nozzle a few times and they were clean on the back each time. Perhaps its some lubricant leaking from factory assembly?
Also since we talking nozzles, I have had the silicone socks rip between the holes, so a good idea to inspect and replace them as needed. I ordered a 20 pack from aliexpress for $10.
Iām wondering if it has to do with heat creep and printing high temperature filaments with left nozzle only. I noticed it happened on mine directly after printing high temp with the left nozzle. So Iām wondering if the filament that was a low temperature in the right nozzle (not in use) is vaporized as it oozed out and hit the blocker plate. Since itās a tight fit between the nozzle and the blocker plate, small vapor sized particles can go up behind the nozzle?
I have only had this issue on the right nozzle
So youāre getting the same crud as I am on your right nozzle?
Yes, I agree. I think this is the next step. Iāll clean everything as best I can and start over. Iāll hold off on the thermal grease for now and just try to more carefully observe under what conditions it re-appears, if it ever does. If it was maybe factory oil that got carbonized, then it wonāt recur.
The first time it happened to me. My pictures looked exactly like yours. I just tried to take it off right now to get a picture for you and I can clearly see I have filament oozing up. I just finished a long print with my left nozzle with high temp only on left. I then did a single print with PETG HF in both. I guess now when I do high temp prints Iām going to be swapping both nozzles instead of just one. When I was doing low temperature prints only. I didnāt have any nozzles sticking. Iāve been having issues with PETG blobing up but the nozzles would never stick. So maybe itās any material that is still on the nozzle (not necessarily oozing out) that then vaporizes and fills the gap as it rises with the higher heat.
Now that I think about it when I did a cold pull for high temperature and I had some low temperature filament in there. I could see crazy amounts of vaporizing going on.
EDIT: I did NOT clean this nozzle manually. This is how it looked with what ever normal printing and cleaning the machine does. So somehow the filament is getting up behind the sock but not completely balling up on the nozzle tip.
I would consider seeing it the problem reoccurs before further action is taken.
Sometimes things happen.
There can be an abundance of caution, but I would utilise those thoughts should a consistent problem persist.
It isnāt like this doesnāt happen normally without issue on other models.
Just a thought.
Looks like you also have the same sensor imprint
What did it look like? Like smoke?
Your photo better illustrates the wicking up of melted filament into the crack than mine did.
Inhale it and try to identify by flavour? 
Heavy heavy smoke that Iām assuming (and could very well be wrong) would also include some vapor sized particles of filament. Either that or maybe the filament oozes up with high enough temperature alone, kind of like solder and flux going to heat.
In both cases it shouldnāt matter too much. Just clean it from time to time would be good enough. You can also apply some thermal paste to get rid of all air gaps if youāre really worried.
Hereās another picture from a different angle. You can see there is some buildup. But itās not like I had a complete blob. I have done zero manual cleaning on this nozzle. Itās somehow working its way up and getting behind the sock.
this is perfectly normal for this style of nozzles, just clean it off if you want to from time to time. itās merely condensation from the vaporised plastics. and it would not matter.
also the temperature sensor donāt care about the air gap or plastic build up you have here. itās mostly being heated by the heating element instead. The nozzle gets heated by the entire contact surface so itās very resilient to these small buildups or air gaps.
a thin layer of thermal grease would help if it worries you, but I wouldnāt bother as high temp thermal grease is expensive lol
