Year 2 and some really hot days this summer and no problems not having the clip on the lower part of the expansion tank. Looks like this may indeed actually be an upgrade! I think I said before, it almost makes sense if the movement with the different expansion rates between he rad and tank isn't enough with the clip installed, and there is really no way that I can see it ever pulling apart given the way it is installed with the upper elbow holding it in place.

So had to replace the rad on the E53 lately and ordered another "Standard Automotive" brand tank, but this one had the slot and clip! So who knows?? maybe the one without the slot was a rebox?? Anyway I ended up not changing the tank on the E53 and am going to leave the one without the clip on the E83.

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1988 325is (purchased new) sold
2004 X5 3.0 2005 X3 2.5
2008 X5 3.0 (new to me)