Moker LS Rear Main Seal Housing Cover — Billet Aluminum Replacement for GM LS1/LS2/LS3 4.8–6.2L, Leak‑Resistant CNC Machined

Moker's billet aluminum rear main seal housing is a direct-fit replacement for GM OE covers (12639250, 12633579) that restores a leak-free seal at the crankshaft outlet on LS-series engines.

If your LS-based Chevy, GMC or Cadillac is showing oil at the rear of the engine, this one-piece cover from Moker gives you a durable, precisely machined alternative to brittle factory cast housings. Built to work across a broad range of LS platforms, the housing replaces worn or cracked originals and helps prevent future leaks that can foul the flywheel, clutch, or surrounding components.

Will this housing fit my LS engine and which OE numbers does it replace?

This Moker rear main seal housing fits most production LS blocks including LS1, LS2, LS3, LS6, LS7 and common truck variants (LM7, LQ4, LQ9). It replaces GM OE part numbers 12639250, 12633579 and aftermarket code 635-518.

• Compatible with 4.8L, 5.3L, 5.7L, 6.0L and 6.2L LS engines.
• Direct-fit for production LS engine blocks—no block modification required.
• Replaces listed GM OE numbers for straightforward purchasing and fitment.

How does the billet construction help prevent leaks compared to the factory part?

Moker machines the housing from high-strength billet aluminum, which resists cracking and distortion that can occur with cast housings under heat and torque cycling. The result is a firmer mounting surface for the seal and a reduced chance of gap formation that leads to oil seepage.

• Billet aluminum provides improved rigidity and corrosion resistance.
• CNC machining ensures flat sealing faces and consistent bolt-hole alignment.
• Pressure-tested tolerances minimize sealing failure under load.

Is this suitable for performance builds or just repairs?

It works well for both: as a replacement for damaged OEM covers and as an upgraded component in high-stress or performance engine builds. The stronger material and precise fitment give added reliability where higher revs and track use demand better durability.

• Ideal for street, towing, and light performance applications.
• One-piece design fits standard LS block geometry for easy installation.
• Recommended when rebuilding an engine or replacing a leaking cover.

Who this is for: Mechanics, DIY enthusiasts, and engine builders working on GM LS-series platforms who need a dependable rear main seal housing that outlasts the OEM cast part. If you’re replacing a leaking or cracked rear cover on Silverado, Sierra, Tahoe, Yukon, Escalade, Avalanche or similar models, or assembling a fresh LS engine and want a stronger, precisely machined housing, this Moker product is designed for your build.