Hi folks,
Thanks for your suggestions...
BobF, no they are not falling apart, I'm not sure about the salt idea, the last few times it was previously used was on fresh water and the tyres tend to get a good washingfrom the bow wave etc.;
tugs46, I'd like to take up that offer, could you tell me the postage and how best for me to pay it... the boats been in partial sunlight and it could well be silicone oozing from the tyres;
meechingman, that suggests it's more likely to be exposure to sunlight rather than water!
Cheers,
Peter