It's often a diester they use to swell the seals slightly.
Quote:
Features and Benefits
Helps extend engine life
Contains seal conditioner to help prevent or control leaks and reduce oil consumption
Helps protects older engines
Guaranteed protection with the Mobil Super Limited Warranty*
Outstanding wear protection under a wide variety of operating conditions
Easy cold starting.
Meets or exceeds the latest industry specifications
API SN / Resource Conserving (Mobil Super High Mileage 5W-20, 5W-30 and 10W-30)
Quote:
Features and Benefits
Helps extend engine life
Contains seal conditioner to help prevent or control leaks and reduce oil consumption
Helps protects older engines
Guaranteed protection with the Mobil Super Limited Warranty*
Outstanding wear protection under a wide variety of operating conditions
Easy cold starting.
Meets or exceeds the latest industry specifications
API SN / Resource Conserving (Mobil Super High Mileage 5W-20, 5W-30 and 10W-30)