An O-ring collar seal for an interface between adjacent first and second components includes a cylindrical structure arranged along a longitudinal axis and characterized by an L-shape in a cross-sectional view. The L-shape includes a first section orthogonal to the longitudinal axis, with a distal end extending toward the axis for being sandwiched between the components. The L-shape also includes a second section extending from the first section, arranged parallel to the longitudinal axis, and configured to retain the O-ring collar seal on the first component. The L-shape additionally includes a round shape third section arranged on the first section's distal end for being compressed by the adjacent components to generate sealing pressure therebetween when the O-ring collar seal is installed in the interface. The first and second sections of the L-shape together define a collar portion and the third section defines an O-ring portion of the O-ring collar seal.