Filter bowl stud corrosion.
Looking closely again at that photo I posted of the failed titanium studs on the S-92 MRGB oil filter housing, I noticed another issue. It appears that the locknuts on those titanium studs are silver plated (MS21043 types possibly?). It is generally poor design practice to use silver plating in contact with titanium, since it has the potential for galvanic corrosion. The lock nuts should have had a dry film anti-seize coating like moly-disulfide, and definitely not silver plate, if they're being used with titanium.
If those locknuts are per OEM requirements, then Sikorsky's engineers definitely should have known better. I wonder if the FAA will catch this one?