If the hoses are original, then replace them both. They have to be in rough shape. Even if it's not the problem, it is still better to be safe than sorry, and you don't want to replace one and then have to do the other later, because you'll have to bleed them again. So, after you replace them, bleed them, bleed them, and bleed them again. I had this problem with my GN years ago, and didn't believe my mechanic when he told me that this could be the problem. As usual, the guy that had been doing it for decades knew more than me, even though I had been fixing brakes for at least 5 or 6 years. Good Luck.
Brian