Update: 10/3/09

Just got done swapping the radiator. Turned out it was the radiator. I took lots of pictures and will put together a DIY. I am surprised that the radiator failed the way it did. In the recent past, it's been plastic end tanks but this radiator is all aluminum yet it still somehow failed.
Failure was on the bottom passenger side. I bought an oem BEHR unit that was 1/2 the cost of the BMW unit. Only difference, the replacement radiator does not have a drain plug. Fortunately, there is a smaller lower hose right under where the drain plug would be, so I can just disconnect it if I ever need to empty out the radiator. I could not afford to tie up the car since its my wife daily driver so I had to complete the job in 1 shot.
Regards.
Raj

All's well that ends well. G/L with the new radiator.

I got the low coolant level warning a few days ago while the car was parked on an extreme angle. Went away for a few days, but now it's showing up while the car is parked level. I don't see any spots where it's leaking any coolant. Here's hoping I don't have a leak somewhere. Car is an '09 with 12,000 miles on it.

Wow that's great information! If you put together a DIY it'll really be appreciated.

Yup - good reminder for out of warranty cooling system (radiator) replacements. I used BEHR's 3-4 times for replacements on my 740's. They seemed to last a bit longer and they even replaced one free that started leaking after about 9 months and 60K miles. Boy am I glad I'm not doing the road warrior routine these days!!

Loss of some coolant is normal. I would strongly suggest you check the level in the resevoir and top it off. Keep an eye and see if it remains the same for some time. Its normal to top off the reservoir with a quart every yr or two. These cars run at high temps so its normal to have coolant loss.
Raj

Thanks everyone.
I promise to write something shortly. I took plenty of pictures so it should help.
BEHR is what came out of the car as well. Looks like they are are oem suppliers to BMW. What was upsetting was the fact that an all metal radiator failed as well. It's always been plastic end tanks in the past but I guess the radiators are just not as good as they used to be yrs back.
On a side note, these failures seem common on BMW but my Porsches have never had issues. I understand that there is a big mileage variance in how often they are driven but needless, I never ever hear Porsche radiators fail.
Raj