Under-hood dip stick cleaners were very popular before the advent of the PCV system.
Cars burned/lost a lot of oil due to engine design, and monitoring the oil was a necessity compared to today.
The cleaner was designed to promote the consumer to check oil without fear of getting oily/dirty, and sold at gas stations, and some were even used as free promotional items.
My buddy has a box full of promo cleaners is the only reason I know this....
