check your hinges! your hinges sit inside a groove and if they`re not a tight fit then over time they will slip forward as they are only secured with small screws (i have seen this before.) you may need to drill an extra couple of holes through the hinge and re-fix but be wary that the hinge runs on a slider and you don`t want the sliding block to hit the new screws.
also your gasket (rubber) may have compressed and may need changing.
5mm does seem alot.
tristian
September 2008