It has been a few months but I think the inner flange ends up inside the outer one. Flanges touching may not be all the way in. I had to lie on my back so I could get one hand on each side of the red hose. I then had to pull down and twist a little at the same time. It was very satisfying when it finally clicked in.

You could also remove the IC and test fit to be sure. May as well change the red post hose gaskets if you have not done it already.

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2009 35d, 2006 325i & 330i