Plus one on Pliobond, if the covering is really lose, take it off and clean all the bits of old glue off both the camera body and the back of the leatherette, then put the Pliobond on only one surface, if you use it as contact cement and apply it to both surfaces and then let it dry to tackiness it will grab hard and leave you no time for you to position the leather. If on the other hand you just have an edge or corner loose work a little glue into the gap with a toothpick and then hold the cover back in place until the glue sets.