Its cold so it leaks.

Thanks for that. The damn thing has been fine all summer. Of course its spent the last two months on bricks so I haven't been riding it. Naturally the first day I get back on the mercury drops to just above freezing. I guess the expansion coeffs of the plastic, retaining bolts or whatever are mismatched in just the right way so to as to allow the bolts to come loose. Having said that, now its been done up in the cold the cover will probably stay tight until it comes off next - probably on the hottest day of next summer.

It may be bollox but as a theory it goes some way to explaining the apparently high failure rate. If the plastic has a relatively high expansion coefficient then when its cold it shrinks to the point where the pressure is taken off the retaining bolts. These are then tightened. When the ambient temp increases the plastic grows again. Of course now its under increased, possibly excessive, compression so the thing warps and lo and behold it leaks again. So we buy a new cover and next winter we start all over again.

If anyone can find the materials spec of the plastic covers it might be an interesting exercise to see what the numbers are and if the theory has any merit. Perhaps I should ask Morton Thiokol. :devious