i have a 94 prelude vtec. my clutch pedal pressure keeps dropping especially when i go on the highway. if i go for a long time, my pedal will fall all the way to the floor. i have to use my toe to get it back up and pump it until there's some pressure again. but this cycle repeats. i just replaced my master cylinder(rebuilt) bout a month ago and clutch slave cylinder about a year ago. i did notice shortage of brake fluid but continues even after refill. this just started happening. the brakes are fine.

 

make sure the line is bleed properly and that there isn't a leak in the hardline or the hose

 

it sounds like a leak somewhere. look out for wet oily spot.

 

Get in the floor board and look up at the piston going in the master cylinder from the clutch pedal.

Feel the surrounding carpet and metal for liquid.