Mercury - Oil Cap Assembly Engine Maintenance Polyamide Resin 8M0142290. Overview. Anyone who has spent time offshore knows that trust in your engine comes from the little things-those parts you rarely think about but rely on every single trip. The Mercury Oil Cap Assembly 8M0142290 is one of those simple but essential pieces that keeps everything buttoned up and running the way it should. When you twist this cap into place and feel it seat securely, there is a real sense of confidence there. It