It occurred to me this morning (while bashing my head against a wall over Jess's saddle niggles) that it may be time to replace my girths, I have 2 synthetic ones with elastic at both ends, both are years old and have done a lot of miles and the elastic isn't exactly 'strong' anymore, as in I can easily stretch it by hand. What is the norm for replacing elasticated girths? or what rule of thumb do you go by?