Last week I replaced my 2015 X5 F15 crankcase breather pressure regulating valve and wanted to confirm that the new regulator was working correctly so bought a $10 oil filler cap and modified it as per the below YouTube video.
Tested it this evening and it is regulating the pressure very well.
https://www.ebay.com/itm/304908625355
https://www.amazon.com/dp/B08MJ76Z18...roduct_details