Endless gum swallowed by old revolutionary, in a manner of speaking (6)
I believe the answer is:
tongue
'manner of speaking' is the definition.
(I've seen this before)
'endless gum swallowed by old revolutionary in a' is the wordplay.
'endless' means to remove the last letter.
'swallowed by' is an insertion indicator.
'old revolutionary in' becomes 't' (I am not sure about this - if you are sure you should believe this answer much more).
'a' becomes 'one'.
'gum' with its final letter taken off is 'gu'.
't'+'one'='tone'
'gu' inserted inside 'tone' is 'TONGUE'.
Can you help me to learn more?
(Other definitions for tongue that I've seen before include "They are hard to say" , "Style of speaking; lick" , "Muscular tissue in the mouth" , "manner of speaking" , "Speech" .)