Thanks to everyone for the input.
The pulley tensioner has been replaced plus alternator and i think only 1 of the idler pulleys.
So you have a similar condition - I hope we can both get this solved! As for the recommendations on cooling system, I've read this everywhere else too and it freaks me out that is going to happen to every e39. I only have 104,000km on the car - should I still make all the replacements? I've done a visual (no leaks) and "felt" the hoses and seem ok, but I really know nothing in the end. My best friend is a mechanic, so I would be saving most of the labour, but I'll have to work out the part costs.
Love this site...great feedback!