Red Line MT-90 75W90 GL-4 Gear Oil – 946ml / 3.78L • 50304 / 50305

Red Line MT-90 75W90 GL-4 Gear Oil – 946ml / 3.78L • 50304 / 50305

Replacement and service Red Line manual transmission lubricant for Mazda MX-5 NA, NB, NC, ND and RF manual gearbox applications listed in the compatibility table.

Red Line MT-90 is a full-synthetic SAE 75W-90 lubricant designed for synchronised manual transmissions and transaxles requiring API GL-4 performance. Its synchroniser friction characteristics are intended to support positive engagement and shift quality while remaining suitable for brass synchroniser components.

This combined listing is available in two selectable container sizes:

• 946ml / 1 US quart — Red Line product reference 50304
• 3.78L / 1 US gallon — Red Line product reference 50305

The listed Mazda MX-5 manual gearboxes generally require approximately 1.8–2.1 litres, depending on gearbox type. Three 946ml bottles are therefore the practical quantity for a complete gearbox service. One 3.78L bottle provides sufficient lubricant for one complete MX-5 gearbox service with fluid remaining.

MT-90 is intended for the manual gearbox only. It must not be used as automatic transmission fluid or as the lubricant for a hypoid rear differential.

Common reasons for replacement include routine servicing, unknown or aged lubricant, contamination, leakage repairs and gearbox removal or overhaul. Fresh lubricant cannot correct worn synchronisers, bearings or other internal gearbox damage.

• Product type: Full-synthetic manual transmission gear oil
• Primary use: Synchronised manual transmissions and transaxles
• Location / system: Manual gearbox
• Brand: Red Line Synthetic Oil
• Product references: 50304 and 50305
• Viscosity / grade: SAE 75W-90
• Specification: API GL-4
• Available size: 946ml / 1 US quart — 50304
• Available size: 3.78L / 1 US gallon — 50305
• Synchroniser note: Designed with synchroniser friction characteristics and suitable for brass synchroniser components
• Application restriction: Not for automatic transmissions or differentials with hypoid gears

Fitment advice: Suitable for the listed manual gearboxes where API GL-4 SAE 75W-90 lubricant is required or permitted. For ND and RF models, Mazda Original Long Life Gear Oil IS remains the preferred factory lubricant for optimum shift feel. For imported, modified or previously repaired cars, matching the required lubricant specification and gearbox type is recommended.

Quantity guidance: Most listed MX-5 manual gearboxes require approximately 1.8–2.1 litres. Select three 946ml bottles for a single complete service, or select one 3.78L bottle where a larger workshop-size container is preferred.

Other items to consider: When changing the gearbox lubricant, you may also want to consider purchasing new drain and fill plug sealing washers, replacement plugs where the existing fittings are damaged, a gearbox oil transfer pump, brake cleaner, protective gloves and absorbent materials.

Useful tools / consumables: A vehicle lift or suitable jack and axle stands, the correct socket or hex tool for the gearbox plugs, a torque wrench, drain pan, fluid transfer pump, eye protection, gloves and workshop cleaning materials.

Difficulty guide: DIY Difficulty: Moderate. Safe access beneath the vehicle, level positioning and the correct fill-level and plug-tightening procedure are required.

Why Red Line? Red Line Synthetic Oil is known for high-performance lubricants, fluids and additives developed for demanding road, track and motorsport use. Red Line products are chosen by enthusiasts and workshops for their focus on protection, thermal stability, shift quality, friction control and application-specific performance.

What’s included: One container of Red Line MT-90 75W90 GL-4 Gear Oil in the selected size: either 946ml / 1 US quart or 3.78L / 1 US gallon. The product quantity is selected using the listing variant options.

Service notes: Loosen the gearbox fill plug before removing the drain plug. Keep the vehicle safely supported and level, drain the lubricant when safely warm, replace sealing washers where specified, fill to the correct service level and tighten the plugs to the model-specific torque. A complete drain and refill is preferred when changing lubricant type. Dispose of used oil responsibly.