Tried to buckle the kids in today ('89 vert) and the rear belt wouldn't pull out more than 4-5 inches, no where near enough to make it over the booster seat. They ride with me probable 2-3 times a week and I've never had the problem before. Anyone know how to make it work smoothly again? And if it needs replaced, what would it take to upgrade to the '90+ 3point design?