If the engine is running fine, that pretty well eliminates head gasket issues. It also minimizes the chance of it being intake manifold ... but not completely. It means if coolant is entering the combustion chamber ... it is a small stream that does not sniff out the combustion.
That leaves the front cover as a likely leaker ... and the intake manifold as a unlikely, but possible, leaker.
Whatever the cause, the water in the crankcase is playing havoc on all crank and cam bearing surfaces ... and will eventually lead to catastrophe.