the early datsun also has the same breather pipe, on the A10 in a datsun 1000 at least

My 63 bluebird 1200 ute only has a breather (No Pipe, dato's at that time wasn't fitted with breather pipes) on top the engine cover & covers oil over the cover & l just wipe it away when l check the oil & water every second or third time, which may be every two months. And yes it gets milky & that when you change the oil in her about 1500 miles! It has 118,784 miles on original engine. The 76 1200 ute l have has 57,378 miles on it haven't seen any oil from breather & it not blocked (yes l checked). Oil changed 1500 miles too & both good the fuel too. Bruns

The issues in question, was a cracked head. It also had a blown head gasket, (Between 1&2) and the head had been burned away where the flame travel hed been.
The cause of the water was the crack.
When I used a b110 inlet manifold on a 310, I had to run the boosteroff the pcv port. I blocked off the rocker cover hole, and ran the lower breather port into the air cleaner. I found that there was quite a lot of "goo" forming on the underside of the filler cap. So Then I swapped the hose onto the rocker cover.
Anyway, a well used motor will generate H20 in the crankcase. Because H20 is one of the byproducts of burning petrol. If your goo is coming out as milky goo, that means it's probably from blowby. Mine was clear in the sight glass, with a thin layer of black (oil) on top.