Picking Out Rear Diff Oil on Redline cant help but look at the oil?

So Im about to purchase Rear diff Oil for my baby, but i cant help but notice when im looking at the engine oil For my Older Brother's Bentley I saw the "suitable for VW/Audi 503.00 and 503.01, as well as Mercedes Benz 229.3 and 229.5" on 0w30 Oil,Strange saw the same spec's For the 0w30 Castrol And 0w40 Mobil Not to start another oil Thread,But I found it weird also i was Debating to use the New Castrol Synthetic Gear oil?

RedLine 75W90 Gear oil.

- Rear differential hypoid gear oil (1) & differential fluid change DIYs (1) (2) (3)

EDIT: See also:
- BMW E39 fluid summary printout for your glovebox (1)

- Differential (conventional, i.e., non-limited-slip E39s): The Bentleys specify "BMW SAF-XO synthetic final drive gear oil" which doesn't exist (it's Castrol). The Bentleys don't specify the weight (it's SAE 75W-90); and the Bentleys don't specify the quality (it's API GL-5 hypoid gear oil). Given that, suitable replacements are Amsoil Synthetic Manual Transmission Fluid (MTF) API 75W90,Mobil1, Royal Purple Max-Gear, & Redline SAE 75W90 API GL-5 synthetic gear oils. Unfortunately, there's no way to tell which of the three (3) different differentials you have w/o looking at the numbers molded into the metal. Bentley page 020-11 & 020-26 & 331-6. [Volume: Type G=1.7 quarts, Type 188 Compact=1.1 quarts, Type 220/215 Compact=1.5 quarts.] Replacement Interval: Lifetime fluid (but most recommend replacing differential fluid at the same time you replace transmission fluid, which is about 5 years or roughly 60K miles).
- Differential (limited-slip E39s, such as the M5): BMW SAF-XJ API GL-5 SAE 75W-140 synthetic hypoid final-drive gear oil (aka Castrol SAF-XJ). This requirement is not listed in the Bentley manual; it is gleaned from the Castrol literature and from what is stated about the M5 in this thread below (please correct if necessary). Replacement Interval: Lifetime fluid (but most recommend replacing differential fluid at the same time you replace transmission fluid, which is about 5 years or roughly 60K miles).

Originally Posted by JohnathanDM

So Im about to purchase Rear diff Oil for my baby, but i cant help but notice when im looking at the engine oil For my Older Brother's Bentley I saw the "suitable for VW/Audi 503.00 and 503.01, as well as Mercedes Benz 229.3 and 229.5" on 0w30 Oil,Strange saw the same spec's For the 0w30 Castrol And 0w40 Mobil Not to start another oil Thread,But I found it weird also i was Debating to use the New Castrol Synthetic Gear oil?

Why are you comparing engine oil when you're needing diff oil?

Originally Posted by DHoang

Why are you comparing engine oil when you're needing diff oil?

Maybe because there aren't enough engine oil threads already?