I've come across a problem with my MCS; after driving for 10-15 minutes the steering becomes very heavy, almost like a car with the power steering off. After I park the car for a few minutes the steering is back to normal and the whole process begins again!

I can't figure this one out, am I missing something very obvious?

 

Not so uncommon!

Mine did the same thing. Got worse and worse until there was no more PS at all. Took it in and they found that the pump had shorted out and the wires to it had actually caught fire damaging the PS hoses also. Fixed for free and have had no problems since.
There have been many threads here on PS problems, so you are not alone. Get in into the shop ASAP and let them fix it. I was lucky that I didn't loose my whole car to fire.

 

Just a quick follow up on my power steering.

I took the car to Asseal BMW(where I bought the car). They claimed they found a loose connection and all was fixed. Shortly after driving the car the same condition returned I brought the car back once more and this time they are replacing the entire pump assembly :smile:

 

The Power Steering can shut itself down if it detects a problem. Best if you get it looked at.

Luke