If you really want to give maximum protection to an M56 manual gearbox then it is worth considering Red Line Lightweight Shockproof 75W140 gear oil at £13.47 plus VAT per US Quart (you need 2 quarts per box). I have been using this in my S70 T5 in the Toyo Modified Production Saloon Car Championship for the last three years and in the S60 T5 we a running in the Britcar Long Distance Series. Both cars are fitted with limited slip diffs., the S60 with a dog box which requires particular protection which only such a formulation can offer.
I keep the stuff in stock.
Regards, Don.Norchi.
www.kalmar-union.com