A sealing washer assembly includes a main washer with a bottom annular groove for a removable O-ring and a top recess for a sealing washer. A fastener such as a screw or bolt passes through the sealing washer and the main washer, into a hole in a mounting surface. When the fastener is tightened, the main washer is clamped to the mounting surface to create a metal-to-metal seal, the O-ring is deformed to create a seal between the main washer and the mounting surface, and the sealing washer is deformed to create a seal between the fastener and the main washer.