The way you wrote this, I thought you'd replaced that stuff after this leaking incident...which is why I wrote what I did.
Yes, the fan failing and you not driving fast enough could cause overheating.
If therm and wp are relatively new, you can hold on them for now, but you need to consider everything...no matter what any fanatic says...it's a system, and you need it all to be there for you!
If AM therm and not OE, that makes it more suspicious. You know Bimmersgarage has great vids for diagnosing leaks/issues with cooling system...I don't know where he got all those naked girl mechanics though!
I just read that there was a separate relay able to be bought for the electric fan, though I think maybe you have an auto and are talking about the fan in front...and I don't know how important that is with cooling issues, but it's there for a reason, I know that!
I'm so depressed. No one wants to come see me. :(
Mangofy your E46!