Genuine Mazda Differential Filler Plug Sealing Washer • 9956-21-800

Genuine Mazda 9956-21-800 Differential Filler Plug Sealing Washer

Replacement Genuine Mazda differential filler-plug sealing washer for Mazda MX-5 Mk2, Mk2.5, Mk3, Mk3.5, Mk3.75 and Mk4 models listed in the compatibility table.

The washer fits between the differential oil filler plug and the differential housing. When the plug is tightened, the soft metal washer compresses against the sealing faces to help prevent differential oil from leaking around the plug.

The washer should normally be renewed whenever the differential filler plug is removed. A previously compressed, distorted, corroded or heavily marked washer may not reseal reliably when reused.

This listing supplies one Genuine Mazda sealing washer only. The differential filler plug is not included and is available separately.

• Part type: Differential filler-plug sealing washer / gasket
• Mazda catalogue description: Gasket
• Primary use: Seals the differential oil filler plug against the housing
• Location: Rear differential filler and oil-level inspection opening
• Material style: Compressible metal sealing washer
• Quantity per differential: 1
• Quantity supplied: 1 sealing washer
• Differential filler plug included: No
• Brand: Genuine Mazda
• Part No.: 9956-21-800
• Also referenced as: 995621800
• Fitment note: Compatible with Mazda MX-5 Mk2, Mk2.5, Mk3 and Mk4 generations
• Exclusion: Not compatible with Mazda MX-5 Mk1 NA models

Important: This washer is intended for the differential filler plug. It should not be confused with the separate washer used on the magnetic differential drain plug.

Fitment advice: Confirm that the vehicle retains the original differential filler-plug arrangement. Where a replacement or upgraded differential has been installed, compare the existing washer dimensions and filler-plug reference before ordering.

Other items to consider: When servicing the differential, consider purchasing the correct differential oil, the magnetic drain-plug washer and a replacement filler or drain plug if the existing threads, sealing face or tool-engagement area are damaged.

Useful tools / consumables: Suitable socket or spanner for the filler plug, ratchet, torque wrench, drain container, fluid pump, cleaning brush, lint-free cloths and manufacturer-specified differential oil.

Difficulty guide: DIY Difficulty: Easy. Replacement is normally carried out during a differential oil service. The vehicle must be raised and supported safely while remaining level so the final oil level can be checked accurately.

Why Genuine Mazda? Genuine Mazda sealing washers are manufactured to match the original plug diameter, sealing face and differential housing arrangement. Correct dimensions and material specification help the washer compress evenly and maintain a reliable oil seal.

What’s in the box: One Genuine Mazda differential filler-plug sealing washer, part number 9956-21-800.

Installation notes: Clean the differential filler plug, sealing face and surrounding housing before installation. Remove the old washer completely and inspect the plug and casing threads for damage. Fit the new washer to the filler plug, refill the differential with the specified lubricant and tighten the plug to the torque specified for the applicable differential. Clean away any spilled oil and inspect the plug for leakage after installation.