if it's been sitting a while the lines might have sludge/ contamination in them. if it's a loooong time the fluid turns to a white chalk. when i start driving a "field special" i take each line loose and clean the lines with alcohol and compressed air. then rebuild each wheel cly.
i noticed you mentioned caliper have you changed the front brakes over to disc brakes? if soit might have something to do with that, if it's been recently changed. good luck
