A retaining ring configured for in-field repair of a fuel injector sleeve upper seal leak, comprising: a circular side wall comprising a barrel-shaped outer surface and a substantially cylindrical inner surface; wherein the outer surface comprises a lower curved portion and a central portion having a curvature that is less pronounced than the lower curved portion; and wherein the lower curved portion is configured to guide the retaining ring into the fuel injector sleeve and the circular side wall has an outer diameter at the central portion that is larger than an inner diameter of the fuel injector sleeve at a location of the upper seal leak such that the retaining ring forces the fuel injector sleeve outwardly at the location of the upper seal leak as the retaining ring is moved into an installed position.