['75 308 GT4 (Peter)]

Clean everything out as best as you can (the hose, air-filter box, etc...) and drive the car for the next while WITHOUT the crankcase breather attached to the air-box. Route the hose to a small plastic bottle (securely attached elsewhere in the engine bay to catch these excess vapours) and see if it dumps that much oil.

I agree with Magoo about the over-filling of oil. A proper-working breather system should really leave only a SLIGHT haze of oil on a surface nearest the hose exit. Too much oil in the case and its just sloshing out in bucket-fulls. The stock breather system works well and as it should. As far as Nick's Krank Vent, its really a gimmick that may work well on Harleys (as the volume of their cranckcases [below the pistons] changes with each revolution, necessitating a heavy-duty venting system), it has little effect on Ferrari engines.

 

['75 308 GT4 (Peter)]

Is the crank vent a compliacated device? Kelly

No, its simply a metal can with tubes running in/out of it. After reading more detail here and at FC, I suspect its not the breather that's faulty, but just a means of delivering this excess oil.

Like Magoo said, the only way to rule out a bad ring situation is to do compression and leak-down tests...