Front Brake Locking Up

Symptoms:

-while riding the front brake engages slowly to the point it locks up completely and doesn't allow movement. It engages without using the lever, riding in a straight line I can feel the engine work harder and harder. •solution: I pulled over and bled the brakes. It eases up and let's me drive home.

This happens over the span of hardly five kilometers.

I've flushed the front brakes. While doing so, I found there isn't any fluid movement into the caliper. I pulled the caliper off and cleaned it, and even with the caliper off there's still no fluid movement to the bottom of the hydraulic line.

My next move is working up the brake line to see where I'm able to get fluid movement.

Does anyone have experience with something similar on this bike? It's got 7,000 Km's it really shouldn't need a new master cylinder yet.

UPDATE:

There was a big ol' air bubble in the master cylinder. Got that out, behaved normally and I was able to get fluid moving through the lines again.

Interesting symptom: the brakes tighten up parked overnight. I'd have to bleed them in the morning, and they're good while riding.