Master Cylinder leaking?

[White70C20]

Last Friday I changed/rebuilt my front drum brakes. I checked to make sure the master cylinder was full when I got done. I drove it around town a little bit and pedal is still soft. It still goes almost all the way to the floor.

Anyway, that's not what I'm asking about today. After I drove it around on Monday, checked the master cylinder to see if it was still full from before I did my brakes. It was at the same level. However, I did notice a drip coming from the underside of the master cylinder near the back.
I had noticed this once before, but the brakes had worked fine until the front shoes de-bonded.
It dripped once or twice in the 5 min I was looking at it. The reservoir is still full. It appears to have a thin amount of brake fluid running down the side of the reservoir in some areas (just a small dribble here and there). I had a new master cylinder put on shortly after I bought the truck a year ago so the reservoir lid/gasket should still be sealing ok right?

The master cylinder fits tight against the booster, so I know it's not leaking there.

As always, any suggestions will be appreciated.

[Wrenchbender Ret]

If it is leaking around the cap, the cap could be warped, the gasket damaged or dirty, or thespring needs tightened up. If it is leaking where it is attached to the booster, then the cup in the master cyl is bad. There is no fluid seal between the MC & the booster.
If your pedal is low you have air in the system or the rear brakes need adjusting.

[White70C20]

Good idea Wrenchbender!

I have checked the master cylinder. It's brand new and not warped. The gasket in the cover is new. It's not leaking from between the master cylinder and the booster.

I was talking to another car guy at the college I'm at and he was suggesting adjusting the rear brakes too. He said since I replaced the front shoes, they aren't having to travel as far as they used to which makes sense. The rear shoes are having to travel farther and they can't do it unless I adjust it.

If that doesn't fix it, I'll have to bleed the brakes. The guy I know has a one-man power brake bleeder made from an old car oil pump. It should work pretty well, but I hope adjusting the rear brakes will take care of it.

[RichardJ]

Get your head out of the sand. Find the leak or replace the MC. Instead of just looking at it while it isn't doing anything, have someone push on the pedal to get some pressure. The pressure will produce a more noticable leak from the line fittings or from the back, between it and the booster.
The diaphram gasket is very important besides keeping it from spashing fluid out. Brake fluid is hygroscopic which means it sucks humidity out of the air. Water is heavier than the brake fluid and begins to settle in the low areas and rust the metal out from the inside. Low areas in the brake lines, bottom of MC bore and bottom of the wheel cylinders will all rust.