Front brake problem

Today I found the front brake lever on my 85 KLR 250 was loose. There is no tension to hold it against the brake lamp switch, so the brake light stays on all the time. I removed the lever hoping to find a spring, but there was none. The master cylinder was about half full, so I topped it off. Then I used needle nose pliers to pull the piston out. It still wont come all the way out on it's own. I replaced the front tire recently, but I've been on at least 2 long trail rides and haven't had any issues. Any suggestions???
Thanks,
C.

Have you thought of an mastercyclinder rebuild? Go to a kaw dealer and order a rebuild kit should be less than $40

What dunkan said for sure. Rebuild kits are relatively inexpensive, can usually find a deal online if you look and don't mind waiting a few days for shipping. When you do the rebuild, make sure you flush the entire system with fresh fluid from a new bottle. Get a big bottle and flush the rear out at the same time.

Fixed for now, anyway. I crack the bleed screw on the caliper to drain the fluid from the master cylinder, and the piston popped back out. I drained the fluid until the master was about half full. Seems to be working now. If it fails again I'll order a kit. The rear is mechanical so less likely to fail.