Guaging Blow By on Detroit 60 Series

I've got a 99 KW with 60 series Detroit I'm selling. My dad drove last 18 years and is retiring. He had engine rebuilt 300k ago and I had it sold but buyer was worried about the blow by. From what I've read it is a common thing with Detroit's. Here is a link from it today while idling after running about 30 min. Any input would be appreciated. Thanks in advance

 

Thanks for response

 

That's what the mechanic at Detroit place told me too. He said if you put your hand over the filler tube and there's no pressure pushing it up your good. If there is pressure could be different things causing it. Got a deposit on it today from a guy familiar with Detroit's. Thanks for the comments.