Hi, thank you for the advice, I would never have known that. I since read on wikipedia that 'Breakage of the belt, because of the nature of the high tensile fibers, is uncommon' , so now I know. The spray seemed to make sense because I can see the way the climate over here degrades rubber; even tires with adequate depth on the tread can need replacing. I've noticed most 'tire sprays' that claim to improve the appearance of tires tend to discolor the rubber. I tried Sonax rubber maintenance spray which seems good but even using that every month, my door seals have dried and cracked a little after 2 years.
At least I asked on here before using the dressing spray, thanks for the info.