You can also put plastic or bakelite knobs in a dish with a couple
denture tablets overnight. I did that with several plastic parts of a
radio I bought from a heavy smoker who had also spilled some soda on the
mic. I jst disassembled the mic and control heads, put the plastic in a
dish with 3 or 4 denture tablets and in the morning rinsed them off and
let them dry the rest of the day. That evening I reassembled the radio
and it looked like it was brand new!