Hy Shellology and guys, firstly residual pressure valves in drum brake master cylinders are not visible, they are part of the internal construction of the master cylinder. Secondly inverted flare fittings [ which is what brake lines and brake system components use ] require NO sealers, or tapes, in fact it is dangerous to use such products in a brake system. If you have leaks, either your components are not tightened together enough, or you have damaged seats or line ends, hope that helps.