Hi Peter,

As to what happened my engine is a bit of a mystery, basically my mate who was home from Oz had my car for a few weeks and the temperature light came on one day.
I dropped it to a garage and they diagnosed head gasket failure. Head gasket was done along with timing chain and other preventative maintenance bits. Long story short car was reassembled but still seemed to have excess pressure in cooling system.
Radiator, water pump, thermostats, aux heater valve and pump, transmission cooler all replaced with genuine bmw parts to no avail (3 different garages)
Was told to drive the car anyway as it wasn't using coolant or overheating, that lasted 4k miles and now we're back to square 1 again. Suspected cracked block.

Patience has well and truly run out with this engine so a replacement in the only way forward really.

It has been a very costly nightmare!