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 key maintenance components required to service Mercury 20 HP and 30 HP four-stroke outboards with serial numbers 0R106999 and above. This complete kit packages the essential oils, filters, cooling system components, ignition parts, and seals required for the recommended 300-hour service interval.. Routine maintenance is critical for maintaining engine reliability, cooling performance, and proper lubrication. By replacing common wear items such as spark plugs, filters, thermostat components, and the water pump impeller, this service kit helps kee