Hi Jim,

I believe that it is. I know of people that use the 0W40 etc etc in them, but most report an increase in oil consumption.

I know that mine is totally intolerant, and even if I use the wrong Castrol 10W60 oil rather than the genuine TWS oil (TWS standing for ten weight sixty!!!!!) it uses significantly more.

Castrol designed TWS for the M range from E36 onwards, so I reckon for the sake of a few quid, you cant go wrong really - it certainly wouldnt hurt from what I have read