For cable your are correct there should be an adjustment nut or mechanisim to adjust it. For hydraulic I'd first check to see if there is any visible dirt or grease below your slave, master cylinder, and on your firewall inside the car. If visibly you don't see any caked dirt or fresh leaking fluid it'd be leaking inside your cylinder. Test this out on a flat parking lot. With the car stopped, foot off the brake, clutch pedal down, gear in 1st, if the car sort of creeps forward either the slave or master cylinder is internally leaking.