OK, I see it now. Mine is black and I never removed it when I took mine apart. Didn't even see it.
I find I need to clean the aluminum tube occasionally as it gets some reclaim on it, but I haven't noticed others mentioning it. Are others needing to do this also?View attachment 6022
Mine's gotten to a similar appearance, I've "deep cleaned" my TM twice and just soaked that piece in ISO each time, but other than that I dont clean it. Actually ironically the other day for whatever reason I was looking at it and just wiped it down with a paper towel really quick.
I think its from getting small crumbs/debris down towards the heater screen, or if the stem is a litttttllle over packed the side wall/o ring "grabs" the extra hairs/crumbs and pulls them out getting them stuck between the stem and wall as you push/pull, smearing it around a bit.
Either way, mines looked similar. Probably not AS build up, but I've definitely noticed some good residue in there