Saltwater intrusion into the bearings....so there is a direct seawater/lube oil cooling system with seawater leaking across the heat exchanger. Seems to me there should be a freshwater system for that application, just for that reason.
I’m not sure enough of the details of the setup to even hazard a guess as to the source of the problem. It does seem strange to me, though, that both the Zumwalt and all of the new LCS-class ships appear to be suffering from the same issue. Design issue? Manufacturing issue?