So, i've been using my cartomizer for a month now, and i have a few questions. I noticed that flipping the little rubber gromet makes a huge difference in taste. But the cotton like filler is what i'm worried about, sometimes when i vape i get random hits of plastic-like throat burn, i started using the other cartridge and now it's fine. Do cartidges have a limited use time and can i replace that filler material?