The most likely cause is not from a manufacturing defect but from a previous restoration/overhaul of the gear.
Part of the blame must rest with the FAA & EASA authorities and others because originally there was no set procedure for a restoration (MRBR/MPD) requirement of the landing gear.
Each landing gear overhaul agency would perform there own procedure as there was never a set procedure to follow.
It was only around 5 or so years ago that authorities brought in set CMM or SB procedures which would be required to be meet, this to allow a FAA 8130 or EASA Form 1 to be issued for a restoration of the LDG to meet the MRB requirements.
This was not just for the Boeing 767 but other Boeing, Airbus and other manufactures aircraft.