Assembly systems and methods are provided for elastically deforming a non-circularly shaped washer while driving the washer through an insertion tool into a workpiece, such as a pressure sensor, having a correspondingly shaped recess with an inner wall diameter less than a maximum radial dimension of the non-circular washer. The washer is released from radial compression into the recess so as to permit the washer to become fixated against the inner wall of the recess by a retention force. The fixated washer has a height greater than a height of the recess inner wall, and may serve as a deformable sealing element between the workpiece and other components.