Hello, just sharing a little trick I just used to effectively clean stained silicone grease from the threads of my demonstrator eyedropper pen.
I have a Franklin-Christoph Stabilis 65, which is clear acrylic throughout.. except for the threads, which were a beautiful shade of Tsuki-yo blue! Cleaning these of silicone grease was really difficult - an old toothbrush couldn't access them very well, whilst a soggy cotton bud just smeared it all around.
Then inspiration struck! (or perhaps it was wind..) Anyway, I rummaged around in my bathroom drawers for an old mascara tube, and scrubbed the wand under running water until perfectly clean. The soft wand bristles are firm enough to poke into the threads but not stiff enough to scratch, and they did a marvellous job of clearing all the old silicone out in just a minute or two!
Hey presto: clean demonstrator. *beams smugly*