Brake fluid leak at Master Cylinder- Booster connection

My brake indicator light went on coming home from work. After inspection, I found a brake fluid leak where the master cylinder meets the brake booster.
I did the basic tests for the booster. 1) Listened for air/vacuum escaping during pedal depression - none all silent. 2) With engine off, depressed pedal, started engine and the pedal went down slightly. 3) Ran engine for 2 minutes, turned off, depressed pedal 3x, each time the pedal rose higher. 4) While engine running, depressed pedal, then turned engine off, pedal did not rise.
Could this be a bad master cylinder O-ring? [ref 90015-AH002] or faulty master cylinder? any ideas?
Thanks.

 

that's the inner seal leaking and fluid comes out the back.

you need to install a new master cylinder

 

yep. bout it. fairly easy to install, pain in the ass to bleed.

 

Was thinking that could be the case, thanks guys.

 

Just replaced mine yesterday. Didn't have a leak like yours, but it looked like it was leaking before. Job is somewhat simple to do. Getting the brake lines back on was a little struggle. Make sure to bench bleed. Will save you a whole bunch of time

 

That was it folks. New cylinder bench bled and installed. Brakes work like new. FYI the autoparts store wanted $10 for a universal bleeder kit that had just one M10 fitting and black hose. I made my own bleeder kit from a short brake line. Cut the ends off with 1" of line both then used clear tubing from Ace, all under $6.