Seal ring Genuine Porsche part 99911329140

Rear Main Oil Seal for Porsche 

Restore engine sealing integrity and prevent costly oil leaks with this OE Match Rear Main Oil Seal for the Porsche 964, Porsche 993 and Porsche 996. Manufactured to OE specifications and measuring 90mm inner diameter, 110mm outer diameter and 12mm width, this critical engine seal is designed to prevent engine oil escaping around the rear of the crankshaft where it exits the engine case and connects to the flywheel assembly.

Fits:

• Porsche 964 (911) C2 1989-93
• Porsche 964 (911) C4 1989-93
• Porsche 964 (911) RS 3.6L 1991-93
• Porsche 964 (911) RS 3.8L 1991-93
• Porsche 964 (911) TURBO 3.3L 1991-93
• Porsche 964 (911) TURBO 3.6L 1991-93
• Porsche 993 (911) C2 1994-97
• Porsche 993 (911) C4 1994-97
• Porsche 993 (911) RS 1994-97
• Porsche 993 (911) C2S 1994-97
• Porsche 993 (911) C4S 1994-97
• Porsche 993 (911) TURBO 1994-96
• Porsche 993 (911) GT2 1994-97
• Porsche 993 (911) TURBO S 1994-97
• Porsche 996 TURBO 2000-05
• Porsche 996 GT2 2001-05
• Porsche 996 GT3 MKI 1999-02
• Porsche 924S 2.5L 1986-87
• Porsche 924S 2.5L 1988
• Porsche 944 2.5L 8V 1982-87
• Porsche 944 2.7L 8V 1988-89
• Porsche 944S 2.5L 16V 1987-88
• Porsche 944S2 3.0L 16V 1989-91
• Porsche 944 Turbo 2.5L 8V 1985-88
• Porsche 944 Turbo 2.5L 8V 1989-91
• Porsche 944 Turbo S 2.5L 8V 1988
• Porsche 968 3.0L 1992-94
• Porsche 968 Sport 3.0L 1994-95
• Porsche 968 CS 3.0L 1993-95
• Porsche 968 Turbo S 3.0L 1993-94
• Porsche 928 4.5L 1978-82
• Porsche 928S 4.7L 1981-83
• Porsche 928S2 4.7L 1984-86
• Porsche 928S4 5.0L 1987-92
• Porsche 928GT 5.0L 1989-91
• Porsche 928GTS 5.4L 1992-95

Diagram Ref No. 21

The rear main oil seal, often referred to as the RMS (Rear Main Seal), is one of the most important sealing components in the engine. It retains engine oil inside the crankcase while allowing the crankshaft to rotate at high speed. A worn or damaged seal can lead to oil leaks, clutch contamination and unnecessary engine maintenance costs if left unattended.

This OE Match replacement provides the correct fit, sealing performance and durability required for maintenance, engine rebuilds and preventative servicing.

What Does the Rear Main Oil Seal Do?

The rear main oil seal forms a seal around the rear section of the crankshaft.

Its primary functions include:

• Preventing engine oil leaks
• Sealing the rear crankshaft opening
• Protecting the flywheel area from contamination
• Maintaining correct engine oil levels
• Preventing oil reaching the clutch assembly
• Supporting long-term engine reliability
• Allowing smooth crankshaft rotation

Without a properly functioning rear main seal, oil can escape from the engine and create a range of reliability issues.

Why Do Rear Main Oil Seals Fail?

Like all rubber sealing components, rear main oil seals are subject to wear and ageing.

Common causes of failure include:

• Heat cycling
• Age-related hardening
• Crankshaft wear
• Engine vibration
• Long-term oil exposure
• Improper installation
• Excessive crankcase pressure
• High mileage use

Over time, the sealing lip can lose flexibility and its ability to maintain consistent contact with the crankshaft surface.

Symptoms of a Failing Rear Main Oil Seal

Common warning signs include:

• Oil leaks between engine and gearbox
• Oil drips beneath the vehicle
• Oil contamination around the flywheel housing
• Clutch slip caused by oil contamination
• Burning oil smell
• Gradual oil level loss
• Oil residue on transmission bellhousing

Because the seal is located behind the flywheel, leaks can often be mistaken for other engine oil leaks unless properly diagnosed.

When Should the Rear Main Oil Seal Be Replaced?

Replacement is recommended when:

• Oil leakage is present
• The gearbox is being removed
• Replacing the clutch assembly
• Rebuilding the engine
• Refurbishing the crankshaft
• Carrying out preventative maintenance
• The original seal shows signs of ageing
• Engine mileage is high

Many Porsche specialists recommend replacing the rear main seal whenever the clutch or flywheel is removed, as labour access is significantly easier during these procedures.

Why Replacement Matters

A leaking rear main oil seal can lead to far more expensive repairs if ignored.

Benefits of replacement include:

• Prevention of engine oil leaks
• Protection of the clutch assembly
• Improved engine cleanliness
• Reduced maintenance costs
• Improved reliability
• Professional rebuild standards
• Long-term sealing performance
• Greater peace of mind

Replacing the seal during clutch or engine work is considered a smart preventative maintenance measure.

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Fits:
Porsche 911 (930) Turbo 1975-89

Click 'zoom in' for large parts diagram.
Diagram ref no 11.

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Diagram ref no 12.

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Fits:
Porsche 924S 1986-88 for Balance Shaft (left)

Porsche 928 1978-82 for Camshafts (need 2)
Porsche 928 1983-86 for Camshafts (need 2) / for Balance shafts cars upto chassis >>82G00071 / >>82G05066
Porsche 928 1987-95 for Camshafts (need 2)

Porsche 944 1982-85 for Camshafts (need 2) / for Balance Shaft (left)
Porsche 944 1985-88 for Camshaft (left) / for Balance Shaft (left)
Porsche 944 1989-91 for Camshaft / for Balance Shaft (left)

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Diagram ref no 18

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Fits:
Porsche 911 3.0L 1978-83
Porsche 911 3.2L 1984-89
Porsche 930 Turbo 1975-89

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Diagram Ref No 33

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Fits:
Porsche 911 1978-80
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Porsche 993 1995-98
Porsche 996 Turbo 2001-05
Porsche 997 Turbo 2007-11
Porsche 996 GT3 2000-01
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Diagram ref no 27

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