I agree that todays oils help a lot but without a closed system my car even with a new engine smelled when I pulled into the garage. I’d does not now with one..
There was no sludge build up in the 50-60’s on properly serviced vehicles including the Fords. Many saw 200,000 miles before needed it anything because they were driven, idled very little, and when driven it was not short trips which killed most of them. Today you must search for non detergent oil; back then it was the most prevalent.
In the60’s when PCV systems started the manufacturing engineers had words for PCV… It was Positively Contaminating Valves. With a minimum of blow-by there would be fewer problems. It there were Zero gap and Total seal rings then we may never have needed a PCV system at all.
56 Vic, B'Ville 200 MPH Club Member, So Cal.