Hearing Martins tale of his loose tow bar reminds me of an incident which might (just, possibly, at a very outside chance) explain his problem. Many years ago I rebuilt my car. It was my pride and joy and nothing was too much trouble. I bought a new bodyshell and transfered everything over to it, rebuilding or replacing every single component. Of course I painted everything I could possibly get with at least one coat of hammerite. When the project was complete I had a car that was as good as new, probably better in many ways. Over the next few months, almost every nut and bolt came loose. After a while I realised that painting evrything meant that components were seating on a layer of paint rather than being bolted up to solid metal. As vibration and operating stresses arrived, the paint gave way leaving things loose. The repeated spanner checks kept me amused for weeks. I realise you lot will say I should have simply wiped the rusty patina with an oily rag but I still maintain the end result was better, once things had settled down that is.
John