I believe the bushes are machined from a casting. I have several with
casting marks on the edge of the hat rim. The only plausible explanation I
can come up with is that due to the machining process for the oil grooves
the spacer face is not square to the centre line of the bush which creates a
slight leverage effect which then fractures the bush at the root of the
spacer which is undercut with no radius . This creates a high stress riser
Geoff Byrne
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