Especially the rear 2 speed derailleur that get fogged up quite easily.
My advice? Buy another one, so you can fit the new one on, and soak the old one properly to removed all the gurk (small flat headed screwdriver work best I have found).
You'll find a small flat headed screwdrivers easier as you can push the gurk out from the side instead of fishing it out from the inside (if that make sense).
Especially the rear 2 speed derailleur that get fogged up quite easily.
My advice? Buy another one, so you can fit the new one on, and soak the old one properly to removed all the gurk (small flat headed screwdriver work best I have found).