As regard coolant leaks there are some weak spots , hoses, thermostat housing, rad cap failing and heater core/matrix last but not least dreaded head gasket! some people only use bmw coolant but ive been ok for years with named ethylene glycol types, hope this helps,,,mine was similar , it was the thermostat husing (tried pattern parts) ended up with genuine which solved it , and it turned out the SAME price.
Ed