Sealing structures and valve assemblies including the sealing structures. The sealing structures include a first body, which defines a first surface. The sealing structures also include a second body, which defines a second surface. The second body also defines a gland, which extends into the second body from the second surface, defines a gland opening on the second surface, and is free of both a tool entry point and a tool exit point. The second body further defines a retention structure projecting partially across the gland. The sealing structure also includes a resilient sealing body positioned within the gland. The retention structure retains the resilient sealing body within the gland, and the resilient sealing body forms a fluid seal between the first body and the second body when the resilient sealing body is brought into pressing engagement with both the first surface and the gland.