In reply to GingerBread22: Very doubtful, if the flex cuff plastic is splitting the boot may have had it, I dont know how old your varios are, but before oyu bother searching out a repair, check strength integrity of boot by sticking shell in the freezer overnight and then hit it with a hammer, if boot cracks, you needed new boots anyway, if not, boot OK look for repair,
Where is it cracking/splitting? you wont get a spare part, but could repair, or even fing a donor cuff on ebay or the like, shells and cuffs cover more than one size normally
HTH