so i use an old otto link hard rubber of my teachers and its looking rancid so i cleaned it in warm water and it discolored, and i have been freaking out and i just used "F21" tire cleaner cause it says it will clean rubber and is non-acid and non-toxic so i tried it and it took almost all the color away and if u use it with a soft bristle brush it helps too and so far it is almost all off. hope this helps. :)

Turned chocolate ? your are lucky, my teacher gave me one old which was green as military, with a very bad taste. I washed up with cold water and soap but it stay dark green !

"I have a Selmer hard rubber mpc for my sop that is less than 3 years old, but has turned that lubberly milk chocolate color". That, my friend is because it is a Selmer piece and it's not made of hard rubber, but rather.....fossilized SHIT!, and that is the reason for the brown color! Ok, I'm joking! Come on, laugh! My guess is that this is a chemical reaction to the acid in your saliva. Try cleaning the mouthpiece with liquid dish soap and a tooth brush. You'll want to clean your mouthpiece with soap and water whenever you're done using it. I would also be sure to swab your horn a couple times and wipe it down with a cloth too.