Subaru OEM Transmission Oil Cooler Union Screw STI 2004-2007 / Legacy GT 2007 | 21663AA010

Overview

The Genuine Subaru OEM Transmission Screw Union for Oil Cooler (Part #21663AA010) is an exact-fit factory replacement component designed specifically for 2004–2007 Subaru STI and 2007 Subaru Legacy GT models. This precision-engineered union ensures a leak-free connection within the transmission oil cooler circuit, maintaining optimal transmission fluid temperatures under the high-performance demands of the EJ257-powered STI. Choosing a genuine OEM part guarantees factory-spec fitment, material quality, and long-term reliability.

Key Features & Benefits

• Genuine Subaru OEM Part – Manufactured to exact factory specifications, ensuring a perfect fit and eliminating the guesswork associated with aftermarket alternatives.
• Leak-Free Sealing – Precision-threaded screw union design provides a secure, oil-tight connection critical for maintaining proper transmission fluid flow and cooling performance.
• High-Performance Application – Engineered for the demanding thermal and pressure environment of the 2004–2007 STI's transmission oil cooler system.
• OEM Quality Materials – Built from the same materials used in original factory assembly, ensuring durability and resistance to transmission fluid degradation over time.
• Factory Warranty Coverage – As a genuine Subaru part, it is backed by Subaru's OEM parts warranty when purchased through an authorized source.
• Direct Replacement – No modifications required; installs exactly as the original component did from the factory.

What's Included

• 1x Genuine Subaru Transmission Screw Union, Oil Cooler (Part #21663AA010)

Specifications

Fitment & Compatibility

This genuine Subaru part is designed to fit the following vehicles:

2007 Subaru Legacy GT

2004-2007 Subaru STI

Always verify fitment against your vehicle's VIN and original part number before ordering. Cross-reference OEM part number 21663AA010 to confirm compatibility.

Installation

This screw union is a direct OEM replacement for the transmission oil cooler circuit on 2004–2007 STI models. Installation involves accessing the transmission oil cooler line connections; it is recommended to drain the transmission fluid prior to replacement to prevent spillage. Torque to factory specifications as outlined in the Subaru service manual. While a mechanically experienced DIYer can complete this repair, professional installation by a qualified Subaru technician is recommended to ensure proper torque and leak-free sealing.