I am having a problem with my 69 SS 350. Oil leaks out of the breather and oil fill hole. I have replaced the pcv and both valve covers, but am still having issues. Any help is appreciated.

 

Do your valve covers have an inner baffle where the breather holes are? If not, and the holes are open into the head, then oil will get sucked straight out of there, causing leaks such as what you have.

 

There are baffles in the valve covers for the breathers

 

The Oil trap, breather, flame trap and PVC are commonly used terms/ parts that basicaly allow for the engine to vent positive crankcase pressures due to blow by from the pistons.
The only way that oil can come out of the breather is if it is overfilled, a lot of people fill the box until the oil is level with the front plug, this in fact is not a level plug but in fact a filler plug, the correct way to test the level is to use a special tool which is basically a dipstick, it go into this breather hole and the level of oil should be about 3 inches below to this plug, in short re check an drain some off and everything will be under control.

http://gmoptimum.com/en

 

^ What?
First off, a breather setup is necessary, NOT because of blow-by, but because of the natural change in crankcase pressures from the pistons going up & down and displacing air.
Since we're referring to oil in an engine, I don't follow what you're talking about when you refer to "the box", "front plug", and "special dipstick to go in the breather hole"?

 

If every thing is operating correctly as camaro 69 is suggesting than try a compression test blowby for one reason or another could cause this.