When they feel stiff or 'strange', I go at them. Amazing what you find. Had an old Barient on my mast that felt funny so I pulled it apart. Found that corrosion between the aluminum base plate and the bronze winch had broken the base of the winch - came off in 5 pieces! Made the overhaul easy - I just replaced it with a Lewmar 16 (with electrical tape on the faying surface).