Main shaft seal. Porsche 911/912 1972-86

Main shaft seal,  23 x 35 x 8/11.
A rubber shaft oil seal (radial seal) for the main/input shaft of a 901/915-series gearbox. It fits around the rotating shaft and seals the interface between the rotating shaft and the gearbox housing to prevent gearbox oil leaks.
Dimensions: 23 mm (shaft diameter) × 35 mm (outer diameter) × 8/11 mm thickness (seal housing/dual-lip design).

Fits:
Porsche 911 1972 - 1973 (TYP 915) from:
G 733 7575 >>
G 723 0507 >>
G 783 0838 >>
Porsche 911 Carrera 1973 - 1986

Diagram ref no 11

This seal prevents gearbox oil from escaping around the input or main shaft, ensuring the transmission remains properly lubricated. It also blocks dirt, water, and other contaminants from entering the gearbox, helping preserve internal components and maintain correct operating pressure. By replacing a worn, hardened, or cracked original seal, it restores a clean, leak-tight barrier for reliable long-term gearbox performance.

Original gearbox seals degrade over time: rubber lips harden or crack, springs lose tension, and sealing surfaces wear. A failing main-shaft seal typically leads to:
• Gearbox oil leaks
• Loss of gearbox oil over time (low oil level)
• Contamination ingress (dirt, water), leading to accelerated gearbox wear or internal damage
• Messy drip underneath the car and gearbox housing

Replacing the seal with a correct-spec new unit restores proper sealing, preserves gearbox oil integrity, and helps prevent costly internal damage or gearbox failure.

You should replace this seal if:
• Gearbox oil leaks are visible around the input shaft or bellhousing area
• There is seepage, oil dripping, or a film of oil on the underside of gearbox or clutch area
• The old seal appears cracked, hardened, or visibly damaged
• You are doing a gearbox rebuild, overhaul or maintenance
• You notice loss of gearbox oil or suspect contamination ingress

Related reference numbers
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99911332740

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