I've had time to have a closer look and think that what may have happened is that the bolts loosened off. These things were tightened down and I used red loctite on the threads. I also used the retaining tabs. The tabs that came with the uni-joint didn't appear to be as good quality as the original ones and the holes that the bolt goes through were a fair bit bigger than the originals. Again just wondering if any of you guys have had similar problems. Given that these four piddly little bolts play such a critical role should checking these form part of a regular maintenance program? As always thanks folks.

Bob