My old one worked exactly the same as the new one. I was chasing some odd trim issues that were likely just worn out cat so I am suggesting as you said loaner for diagnosing but also say your knock off works perfectly for a month and craps out. Mine is just sitting on a shelf and doesn't fit in either of our new x5s so I would send to anybody that could use it.

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