I have open motorsport breather caps on my '84 carbed engine and with 150,000 miles it doesn't spit any oil onto the engine (i think it'd be kinda hard to because there's a big baffle underneath the cap opening to keep oil from sloshing up), and the GT has 115,000 miles and it hasn't had any problems yet to my knowledge.
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previous name: 84stangLX
'84 Mustang 5.0 LX
my LX
'89 Mustang GT
my GT