Just had a failed print, and the head ended up accumulating a sizable blob of nGen. It managed to ooze inside the sleeve on the nozzles. When I heated up the nozzles to remove the plastic, the blob dropped off after about 30 seconds, and brought the sleeve with it. The portion of the sleeve in the back of the nozzles got extremely brittle.
It’s purging just fine right now, so I guess all I lose is some speed in heating up. Always be vigilant!