SMG playing up - M3 (Std non CSL)

[Pip1968]

My son in law to be (possibly ) has been having trouble driving back from Birmingham. The car seems to lose power whilst he is driving and kicks into ' Neutral' and then a short while after realizes it is still moving and goes back into '3' or '4' et cetera.

I have tried a search on here but the facility does not seem to like the 'word' SMG for some reason.

Online I can see others who have said they have had problems with SMG that have been solved by a new relay. He has looked at the reservior and it seems low but online people seem to say that the level depends on the engine being on or off and the pump having been actuated or otherwise.

Anyone have any obvious solutions or has anyone had the same issue?

Anymore information on the reservior level would be interesting too.

Pip