For stuck ones I have found using a thin flat screwdriver in the groove around the top under the clamp ring and wiggling easiest to get out stubborn ones.
Mine is dead, done all the cleaning malarky, even in me sonic cleaner, but rarely works.
I have now bought a brand new KA one, making a fitting with the pipes etc on it, will block the hole feeding iscv but use the outlet from it to admit new air from new iscv, tiny air filter on other side, all hidden on underside plenum, only difference would be pipe leading from present iscv to underside of plenum, but for £18 brand new delivered why not ?
tabetha