I've had this happen on a friends 1200 coupe & it was worn seals in the master cylinder itself, not the front brakes. Replace the master cylinder with a new one, 11/16ths or 13/16ths, depending on the size of the rear wheel cylinders. Match the size of the M/C to the size of the rear wheel cylinders. Make sure the master cylinder is to suit front discs, a 1200 ute usually has front drums & the front circuit has a residual pressure valve that'll cause the front brakes to drag & sometimes even lock up. So, for the 11/16ths, ask for a Datsun 1200 Coupe Master cylinder. For the 13/16th's try for an early 120Y Master Cylinder. You could also ask for a Sunny M/C, but you'd have to install the rod that goes to the pedal. Also, when bleeding the brakes, don't forget to bleed the master cylinder itself. just run a clear line from the bleed nipple back into the reservoir, then pump the pedal a few times til the air bubbles go away. Brakes are one of the things I don't skimp on, because not being able to stop the car is a nasty feeling, & you sometimes don't get a chance for that second pump on the pedal.