Months to drop suggests a weak seal in a valve somewhere. I drive past some undriven BMWs that are sitting on their bump stops I think it's not all that uncommon.

I've left my old e53 sit for about two months without driving and it held (was about 17 years old at the time). I'll be curious to hear if people have had leaks other than the air SPRING (Airbag are what catch you in an accident).

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2011 E70 • N55 (me)
2012 E70 • N63 (wife)