The cap holding a bit of vacuum that collapses the hose has nothing to do with it being faulty. In fact the cap which doesn't hold a bit of vacuum is more likely to be faulty and not allow pressure to build which is the primary function of the cap. It would be nice if they designed the cap so that the vacuum valve would work with gravity and not need a spring but it's probably not considered a "positive" enough seal. The cap that doesn't collapse the hose probably(hopefully) just has a weaker spring on the vacuum valve.

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