A crack? Just put a strip of Eternabond tape over it, or a lot of Dicor lap sealant.
Is this crack in the roof membrane, or in the sealant along the edges or seams? You don't need to re-coat a rubber roof unless the EPDM membrane itself is worn through, i.e. you can see the weave of the backing material. Cracks in the caulk/sealant just require re-caulking.
If your membrane is worn down (and it might be on a 1998), you can apply a coat of Liquid Rubber, Kool Seal RV, or similar EPDM compatible product.