Michigan Motorsports Gen 3 LS Valley Cover Gasket for 1997–2007 LS1/LS6/LM7 – Molded Rubber, OEM Fit (Replaces 12558178)

The Michigan Motorsports Gen 3 LS Valley Cover Gasket is a direct-fit replacement gasket engineered to seal the engine valley on 1997–2007 GM Gen III LS engines and replace GM part 12558178.

This molded rubber valley cover gasket is made to match OEM dimensions and sealing characteristics, giving a dependable barrier between the valley cover and the block on LS1, LS6, LM7, LQ4, LQ9, LR4 and many other Gen III platforms. It’s intended for engine reseals, cam swaps, valley cover upgrades, or routine maintenance where oil containment and consistent sealing are required. Built with a precision-formed sealing bead and durable rubber compound, the gasket resists heat, oil, and vibration common to high-use street and performance applications.

How does this gasket match OEM fit and function?

The gasket is molded to the original GM profile and engineered to replace part number 12558178, so it installs in the same orientation without modification. Dimensional accuracy and the integrated bead provide the compression and contact needed for a reliable seal between the valley cover and block.

• Exact-profile molding for direct replacement of GM 12558178
• Integrated sealing bead to ensure uniform compression
• Available for all 1997–2007 Gen III LS blocks and valley covers

Will this gasket prevent oil leaks after cam swaps or reseals?

Yes—when installed correctly, the gasket’s molded rubber and bead form a consistent oil-tight interface that minimizes seepage points. Proper surface prep and torque sequencing are still required to achieve a lasting leak-free installation.

• Molded rubber resists oil-related swelling and degradation
• Bead design concentrates sealing pressure where leaks commonly start
• Works with standard torque values and OEM installation practices

Which Gen III LS engines is this gasket compatible with?

This gasket covers a broad range of Gen III applications from 1997 through 2007, including iron and aluminum block variants. It fits popular factory engines and many swap builds that use the Gen III valley cover geometry.

• Compatible with LS1, LS6, LM7, LQ4, LQ9, LR4 and other Gen III engines
• Fits both stock and many performance-oriented valley covers
• Suitable for OEM rebuilds and aftermarket conversion projects

What materials and durability can I expect from this replacement gasket?

The gasket is produced from a heat- and oil-resistant rubber compound with a precision-formed sealing bead to maintain a long service life under typical automotive conditions. It is designed to withstand engine bay temperatures, vibration, and repeated thermal cycles without losing sealing integrity.

• High-quality rubber for oil and heat resistance
• Molded bead helps prevent distortions and keeps consistent contact
• Manufactured to meet or exceed OEM standards for longevity

Who is this for: The Michigan Motorsports Gen 3 LS Valley Cover Gasket is aimed at professional mechanics, DIY enthusiasts, and engine builders working on 1997–2007 GM Gen III LS engines. It’s especially useful during camshaft installs, valley cover replacements, full engine reseals, and any project where OEM-fit sealing is required. If you need a reliable, direct-replacement gasket that matches factory fit and performance without modification, this gasket is built for your Gen III LS application.