Pipe thread fittings are self sealing by design and the brass fittings for brake and fuel lines do not require sealants if they are properly cleaned and in good condition. (Sealants are used in iron fittings are used because of the porosity of the metal and the roughness of the threading action.) If they are not, I replace them. If you notice, any flare fitting uses SAE thread and must be torqued sufficiently to compress the flare for proper sealing. The final torquing of the pipe threads is "compressing" the threads thus providing the sealing function.