5000309 Gearcase Seal Kit for Johnson Evinrude | JLM Marine

Gearcase Seal Kit for Johnson Evinrude Outboard Lower Units – OEM 5000309 / Sierra 18-8383

This gearcase seal kit is designed for Johnson and Evinrude outboard lower units, covering a wide range of 2-stroke models from 40 HP to 75 HP with large housing configurations. Engineered to restore factory sealing performance, this kit ensures reliable protection against water intrusion and gear oil leakage in demanding marine environments.

This aftermarket replacement kit directly replaces OMC Johnson/Evinrude 5000309 and Sierra Marine 18-8383, providing a cost-effective solution for lower unit maintenance and repair.

• Complete seal kit for lower unit gearcase applications
• Fits multiple Johnson/Evinrude 2-stroke models from 1985–2009
• Designed for large housing lower units

Part Number Cross-Reference

Use this table to confirm equivalent part numbers across OEM and aftermarket brands.

Compatible Engine Models

Confirm your engine model/year in the table below. For Johnson/Evinrude owners, here's a guide to help you identify your engine's serial/model: Johnson/Evinrude Serial Number Guide.

Technical Specifications

Package Contents

This kit includes all seals and components required for lower unit gearcase service as shown in the product images:

• 1 × Seal Kit Lower Unit Gearcase (complete kit with all seals and components shown in images)

Installation Guide

1. Disconnect the spark plug wires to prevent accidental engine start. Drain all gear oil from the lower unit completely.
2. Remove the propeller, then unbolt and separate the lower unit from the mid-section following your service manual.
3. Disassemble the lower unit gearcase, taking care to mark component positions for reassembly. Remove the drive shaft and propeller shaft.
4. Carefully remove all old seals, o-rings, and gaskets from the gearcase housing using appropriate seal removal tools.
5. Thoroughly clean all sealing surfaces, removing any residue, corrosion, or old gasket material. Inspect components for wear or damage.
6. Install new seals from the kit using the proper seal driver tools to avoid damage. Apply marine-grade grease to seal lips as specified.
7. Reinstall the propeller shaft and drive shaft, ensuring proper alignment and engagement of gears.
8. Reassemble the gearcase components in reverse order of disassembly, referencing your markings.
9. Reattach the lower unit to the mid-section, torquing all fasteners to manufacturer specifications.
10. Refill the lower unit with the correct type and quantity of gear oil through the fill port.
11. Check for proper gear oil level at the vent hole. Reinstall the propeller and reconnect spark plug wires.
12. Perform a water test to verify proper sealing and operation, checking for leaks or abnormal noise.

Troubleshooting & FAQ

Q: How do I confirm this seal kit fits my specific Johnson or Evinrude outboard?
A: Verify your engine's horsepower, stroke type (2-stroke), year, and confirm it uses a large housing lower unit. Cross-reference your current OEM part number (5000309) or check the compatibility table above. If your model/year matches and you have a large housing configuration, this kit will fit.

Q: What are the signs that my gearcase seals need replacement?
A: Common symptoms include visible gear oil leaking from the lower unit, milky or contaminated gear oil (indicating water intrusion), difficulty shifting gears, or unusual noise from the lower unit. Regular inspection during oil changes is recommended.

Q: How often should I replace the lower unit seals?
A: Replace seals whenever you perform major lower unit service, such as water pump replacement or gear repair. Preventive replacement every 3-5 years or if you notice oil contamination is good practice, especially for motors used in saltwater environments.

Q: Do I need any special tools to install this seal kit?
A: Yes, proper seal installation requires seal driver tools of appropriate sizes, a torque wrench, and potentially a bearing puller. Marine-grade grease and the correct gear oil are also necessary. Consult your service manual for specific procedures and torque specifications.

Q: What's the difference between this aftermarket kit and the OEM version?
A: This listing is an aftermarket replacement part (not an OEM component). We build to OEM specifications using comparable-grade materials. Production is done in an ISO9002-certified facility, and each batch is inspected for consistent performance.

Q: How fast do you ship and how much does it cost?
A: We offer fast global shipping—typically 5–15 days worldwide—and standard shipping is free. Expedited options are available at checkout depending on your location.

Q: What is your warranty and return policy?
A: This product includes a 1-year warranty against manufacturing defects under normal use. If something goes wrong, contact our support team with your order details. Returns are accepted within our standard return window (unused & in original condition); please see our policy page or reach out for instructions.

Important Notes

• Verify that the product images and specifications match your original part. If discrepancies exist—even if your model is listed—do not proceed with the purchase.
• This product is an aftermarket replacement part and is not an OEM component.
• Professional installation is recommended to ensure safety and optimal performance.

Why Choose JLM MARINE?

• Quality Assured: As a trusted manufacturer for over 20 years, we supply top marine brands globally.
• Fast Global Shipping: Free delivery worldwide in 5–15 days.
• Direct from Manufacturer: Competitive pricing without compromising quality.