Both the seals are equally critical, they’re just o rings on the ends of a pipe. And they both have weep holes to allow seepage to exit the engine. You don’t want leaking coolant to stay in the engine.

But you’re correct that the front one fails more frequently and prevention using the stent pipe is prudent and can stabilize sketchy seals. TheBimmerfix pipe is a good product and I’d start with that if the rear seal isn’t leaking yet.

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2005 X5 4.4i SterlingGrau, Sport Package, DSP
Build 3/12/2005