Titanium fasteners (like Hi-Lok pins) are commonly used on aircraft structures. But only for applications where they are not normally intended to be removed. They work well in situations where they are installed using carefully controlled procedures.
As soon as the MRGB oil filters were being changed out far more frequently than initially designed for the studs should have been reviewed. Swiss cheese hole #1
As soon as two out of three studs snapped on the Broome flight in July 2008 the studs should have been changed out immediately. Swiss cheese hole #2.
Swiss cheese hole #3 unfortunately took away 17 lives, completely avoidable, more souls would hopefully have survived had the PIC put her down instead of dropping to 800 ft and speeding back at 133 kts for dry land.
I was on that a/c coming back from offshore just 3 days prior to 491 and I lost a lot of good friends and work colleagues that day, IMHO all because the warning signs on the studs were not addressed properly. That is the hard lesson that should have been learned.
Now we have the TRPCS saga back to haunt us after initially rearing its ugly head in 2007. No root cause failure, just increase the awareness and inspection frequency, drop the HUMS IMD threshold from 2.5 to 1.75, update the SGBA algorithm, await the manufacturer's analysis and findings from the inspection/new HUMS threshold failed bearings.
So what is the issue, long-term storage and breakdown of TRPCS seals wet, dry , half-full, hydroscopic/dust particles ingress, supplier material issues, who knows, we certainly don't this side of the fuselage...