it is not a gasket that holds the top portion on. it is just a black sealant type glue similiar to RTV. go to benz and get a tube of the black sealant used to reseal the rear diff. they'll know what your talking about!
be careful when tightening the little allen bolts and taking off the rubber hose. these can all break very easy. after taking the rubber hose off and all the bolts that hold the cover on, take a big flathead screwdriver and carefully pry the cover up. pry from where the rubber hose went and use the fuel rail as leverage but i repeat "carefully". it will take a few minutes but it will break free. after taking the cover off take a pocket screw driver and a razor blade and clean the grooves completely to get rid of all the old glue! you'll see when you get it off!
Jason