Front brake lever jurk.

[PieEater]

Cleaning and lubing the pivot bolt is a good shout if this doesn't work you could take the calipers off and see if all of the pistons are moving relatively freely, the piston seals if they haven't already been replaced will be long past their best and may be causing the pistons to bind or seize. Another possibility is the master cyliner, you can get a repair kit fairly inexpensively but I would check the stuff that you can do without spending any money first.