currently running SAE 30 royal purple in my 6 hp briggs push mower. satisfied with the oil, no cpmplaints but have heard bad things about royal purple, so i was wondering, would it be okay to run german castrol 0W30 or amsoil 5W30 in it? ive heard many good things about GC 0W30 in auto engines just want to make sure its ok for my push mower.