This is the answer i got from Paul Jacobs:
I was at Bills workshop only yesterday to discuss the risers with him and without being able to examine any in situ, he is still at a complete loss as to why a couple should fail if they were tight at all times.
He feels that if they are allowed to become loose, this would then contribute to metal fatigue as it is moved back and forwards each time the steering is turned, but if the face of the riser is tight to the steering arm, there can be no movement, so no metal fatigue.
He did wonder if the powder coating on the steering arm had disintegrated after the riser was fitted, this would then allow it to move slightly? If it is tight then there should be no rust showing. He also suggested that if there is any gap whatsoever, it could then sit on a hardened steel thrust washer of the appropriate thickness to fill the gap.
He has consulted his CNC supplier who categorically states that the force needed to sheer the riser, if properly tightened would be around 3 tons [3000kgs?] which is quite some force and beyond what would need to be applied to turn the steering arms in normal use.
As I stated in my post, if people are concerned, they must stop using the riser and return to the standard track rod ends, although this will of course return partially to the problem of bump steer, unless the car ride height is lowered.
