Want to know more about how your engine is breaking-in or wearing? Curious about whether or not your oil is doing its job? Want to be ahead of problems that may develop? PartsVu has partnered with Blackstone Laboratories and we are now offering professional oil analysis kits. Results are typically received in a few days via email. Shop now.Mercury 300 Hour Service Kit 20/30 HP 8M0120839. The Mercury 300 Hour Service Kit - 8M0120839 provides the essential maintenance components required to perform the recommended 300-hour service on Mercury 20 HP and 30 HP four-stroke outboards with serial numbers 0R106999 and above. This complete kit combines the critical oils, filters, cooling system components, ignition parts, and seals required to keep your engine operating reliably.. Routine service intervals help maintain proper lubrication, cooling efficiency, and overall engine performance. By replacing common wear items such as spark plugs, filters, thermostat components, and the water pump imp