Dont hold me to it but I believe that Dubarry will repair them - dont know if they would charge though (shouldnt do after only 18 months) I have Dubarrys and have treated them very badly but they are still intact after 3 years +.
Never had a pair of durbarrys so can't comment on them. I did though have a pair of HH long boots that split at the seem and the cobbler fixed them. And if the cobbler can't fix them a good saddler should be able to.