Why is my oil breather cap spilling oil on to my valve cover?

Does it need cleaning and if so how? Or should I replace it? Also, when I stop the engine, vapor comes out of the oil breather cap. How much is normal?

The cap looks to be in good shape. This is on a 1960, 235 six. The engine runs great otherwise.

Thanks.

1960 Chevy Apache 1/2-ton
1965 Chevy Half-Ton Suburban
1966 Chevy C60 2-Ton

Stupid is as stupid does. - Forrest Gump