Experts to keep on retaining old fools (8)
'fools' is the definition.
(buffoon is a kind of fool)
'experts to keep on retaining old' is the wordplay.
'experts' becomes 'buffs' (I've seen this before).
'to keep' is an insertion indicator.
'retaining' indicates putting letters inside.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'on' enclosing 'o' is 'oon'.
'buffs' going around 'oon' is 'BUFFOONS'.
(Other definitions for buffoons that I've seen before include "Rude or vulgar fools", "Clowns or dolts".)