I saw the DIY for a coolant flush and it was really intense...and involved jacking up your car, removal of intricate parts and hoses that would need to be replaced and re-calibrated with precise calculations.
So I went to Strauss Auto and they did it for 30$ as part of a regular oil maintanence (some of you from BMW-Forums may remember this drama i had last november) but they put in the green-nasty coolant that tends to fcuk up BMW's hoses after awhile....I did not want that stuff in my car...
So I had some extra cash and took it in to BMW dealership and got a full coolant system flush and fluid replacement, engine bay wash and car wash for $125.
Pricey...eh?....but it was worth it and whats better is BMW dealrship work comes with warranties so if anything happens my car is going back to them....