Mercury - 300 Hour Maintenance Kit FourStroke Service Package Complete Engine Care Components 8M0120837. Overview. There's a special kind of pride that comes from owning a small FourStroke Mercury outboard. These engines aren't loud or flashy-they're quiet workhorses that faithfully push you across glassy coves, help you troll the shallows, or carry you to that tucked-away spot only a few people know about. But even the most reliable outboard needs the occasional deep service, and when the 300-h